Volume 10, Issue 4                                                                                                     April 19, 2002


Vegetables

Vegetable Insects - Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu

 

Cabbage.

Imported cabbageworm and diamondback moths have been observed laying eggs in cabbage, so larvae should be detected this week. Once DBM eggs hatch, young larvae will first mine between the upper and lower leaf surfaces before moving to the heart of the plants. Treatments should be applied when 5% of the plants are infested with larvae and before larvae move to the heart of the plants. Avaunt, Bt insecticides,  Proclaim, or Spintor will provide effective control of both species.  Be sure to rotate between these classes of insecticides to avoid the development of resistance.

 

Peas.

Be sure to watch for pea aphids in your earliest plantings of peas. The recent weather has been favorable for aphid development. As the weather fluctuates between the current hot temperatures and anticipated cool weather next week, aphid populations often explode and beneficial insect activity can lag behind. On small plants, you should sample for aphids by counting the number of aphids on 10 plants in 10 locations throughout a field. On larger plants, take 10 sweeps in 10 locations. A treatment is recommended if you find 5-10 aphids per plant or 50 or more aphids per sweep. Dimethoate or Lannate will provide aphid control. Be sure to check the labels for application restrictions during bloom.

 

Sweet Corn.

In addition to cutworms, be sure to watch for flea beetles on your earliest planted corn. A cutworm treatment should be applied if you find 10% leaf feeding or 3% cut plants in one-two leaf stage corn. A pyrethroid will provide effective control. Fields should be treated early in the morning or in the early evening when cutworms are close to the soil surface to achieve the best control. In order to get an accurate estimate of flea beetle populations; fields should be scouted mid-day when beetles are active. A treatment will be needed if 5% of the plants are infested with beetles. A pyrethroid or Sevin will provide control.

 

Potatoes.

Since we currently have a number of insecticides labeled on potatoes (Actara, Fulfill and Provado) that move into the leaf at application (translaminar), it is important to consider which fungicides are used in combination with these insecticides. The most effective control will be achieved when translaminar insecticides are able to penetrate the leaf surface. Therefore, these materials should not be combined with "sticky fungicides" such as Bravo Weather-Stik or spreader-stickers that might prevent movement into the leaf.  If you plan to use a translaminar insecticide in combination with a fungicide, then select a fungicide that does not contain a spreader-sticker like Dithane, Polyram, Quadris, or Bravo Ultrex.

 

 


 

Vegetable Diseases -  Kate Everts, Extension Vegetable Pathologist, University of Delaware and University of Maryland;  everts@udel.edu

 

 

Many abiotic problems (scorch from high temperatures, excess nutrients and chemical burn) may cause spots on the leaves of plants in the greenhouse.  There are also several seedborne watermelon diseases that may show up on seedlings in the greenhouse.  Gummy stem blight (GSB) is the most common, but Alternaria leaf blight and anthracnose also affect watermelons.  There are several greenhouse practices that minimize infection by the pathogens of these diseases, including GSB.  The greenhouse should be disinfected before planting (benches, walls, walkways, etc.).  The seed source should have tested negative for the pathogen with a minimum assay number of 1,000 seeds.  Use clean transplant trays (disinfect trays if they will be reused) and new soil.  Destroy any volunteer seedlings and keep the area in and around the greenhouse weed free.  Avoid overhead watering if at all possible, or water in the middle of the day so that the plants dry thoroughly before evening.  Keep relative humidity as low as possible through proper watering and good air circulation in the greenhouse.

 

As the seedlings develop, inspect them carefully. Infected seedlings will have small brown lesions on the leaves and water-soaked lesions on the stem. Initial infections will occur as ‘foci’ or clusters of diseased plants. 

 

If the seedlings have lesions or appear diseased, destroy the flats where any seedlings show symptoms.  Remove adjoining flats to a separate area for observation.  Monitor these seedlings daily and destroy those that develop symptoms.  Do not ship any trays containing plants with symptoms of GSB.  Spray with a labeled fungicide when symptoms are observed and continue until plants are shipped.

 

Bacterial fruit blotch (BFB) of watermelon is caused by a bacterium that may also be seedborne.  Initial symptoms of BFB are water-soaked areas on the lower surface of the cotyledons.  Lesions turn necrotic often with yellow halos, are frequently deliminated by veins and subsequently the seedlings collapse and die. 

 

There are only a few fungicides that are specifically labeled for greenhouse use on vegetable transplants.  Dithane F-45 and some copper formulations are labeled.  Do not use Quadris or Bravo; use in the greenhouse is prohibited for these fungicides. 

 

 


 

Pickling Cucumber Rotations - Ed Kee, Extension Vegetable Crops Specialist; kee@udel.edu

 

Pickle growers are reminded to rotate as best as possible.  This is especially helpful in avoiding phytophthora outbreaks.  Phythphthora overwinters and is present at various levels throughout the year.  A three year rotation away from cucurbit crops, peppers, tomatoes and potatoes is helpful.

 

  


Vegetable Diseases -  Bob Mulrooney, Extension Vegetable Pathologist, University of Delaware  bobmul@udel.edu

 

Potatoes.

Foliar fungicide programs for potatoes. Fortunately, we had another year free of late blight and the prospect of late blight occurring in Delaware is very low. The only source of late blight we have, as best I can tell, is infected seed potatoes. Seed growing areas have been free of late blight or have controlled it to prevent tuber infection. Without the threat of late blight what other foliar diseases or diseases that can be controlled with foliar applied fungicides should we be concerned about? Early blight is a disease that we see late in the season on our early maturing varieties that rarely causes problems except on a few susceptible varieties, such as BelRus, Norkotah Russet, and Snowden. Fungicide applications for early blight can be delayed until the later part of the season to prevent premature defoliation on susceptible varieties. The EDBC fungicides (Dithane, Polyram, Pencozeb, Manzate), chlorothalonil (Bravo, Equus, Echo) and Quadris all provide good control of early blight here. Pink rot is a soilborne disease that we have not seen much recently, but some growers have had problems with some fields or low areas in fields over the years. Two applications of  Ridomil Gold MZ, Ridomil Gold/Copper, or Flouranil are recommended when tubers are nickel-sized and two weeks later if you have a history of pink rot. Now growers have the option of applying Ridomil Gold or UltraFlourish in the row at planting as well. Recent research has shown that strobilurin fungicides such as Quadris are also effective in controlling a disease called black dot. This disease is present in every potato field that I have ever surveyed, but it is not known to reduce yields in this area. The fungus is soilborne in old potato debris and seedborne as very small sclerotia. Symptoms appear late in the season on stressed potatoes (heat, poorly drained soil, low nitrogen), but could be confused with early dying because the fungus does some of the same things that Verticillium does to potatoes. Longer season varieties are also more prone to increased levels of black dot. The yield response that has been seen ocassionly when Quadris has been applied to potatoes in the absence of early blight (which it controls extremely well) has been attributed to black dot control. For control of early blight and black dot during the period of rapid growth consider 2-3 applications of Quadris beginning at bloom alternated with Dithane or Bravo every 7 days if black dot is suspected. Those are the primary potato diseases growers need to know and decide what type of fungicide program they need for control. Weather patterns, cropping history and diseases that you have seen on your farm can help you decide what you need. I would recommend several early season applications of either Dithane or Bravo. Once potato rows touch it is difficult to get fungicides to the lower leaves and older tissue is most likely to get infected first with late blight or early blight so at least one application should be made prior to row closure for insurance. None of these foliar applications will control Rhizoctonia. Our use of mostly early maturing varieties, lack of significant levels of early blight, and the absence of late blight is a good reason to re-evaluate fungicide use on potatoes and use only what is needed to produce an excellent crop profitably.

 

 


Field Crops

 

Field Crop Insects - Joanne Whalen, Extension  IPM Specialist;   jwhalen@udel.edu

 

Field Corn.

Black cutworm moth activity reached peak levels in pheromone traps in the Bridgeville, Dagsboro, Little Creek and Wyoming areas at the end of last week (April 12). If you look at accumulated degree-days since peak activity, we should reach 200 DD base 50 by the end of this week (April 19). Although we can see leaf feeding earlier, we generally do not see cut plants from black cutworms until we reach 300 DD from peak catches. Often, early cutting occurs from variegated cutworm that we can find while sampling for grubs.  Since the weather forecast calls for cooler weather next week, we should not see cutting activity until the end of April or first of May. However if the weather remains warm, we could see cutting activity on early-planted corn by next week. A treatment should be considered in 1-2 leaf stage corn if you find 3 % cut plants or 10% leaf feeding.  Pyrethroids provide the most cost-effective control. For the most recent pheromone trap catches, see trap catch table on page 5 of the newsletter or check our website at http://www.udel.edu/IPM/traps/currentbcwtrap.html.

 

Small Grains.

We can now find cereal leaf beetle larvae in barley and wheat in Kent and Sussex Counties. If you are growing high management wheat, a treatment should be considered if you find 25 eggs and/or larvae per 100 tillers and at least 50% of the eggs have hatched. If fields are scouted on a routine basis, a threshold of 0.5 larvae per stem  (flag leaf and next 2 stem leaves) and 10% defoliation can also be used. Lannate, Mustang or Warrior will provide effective control and will also provide control of any worms that have hatched. Lannate is labeled on both crops. Mustang and Warrior are only labeled on wheat.  Sevin will also provide control; however, it can only be applied to wheat and we have seen aphid outbreaks after Sevin use. Furadan will also provide control, but it can not be applied after heads emerge from the boot. True armyworm moth catches have increased significantly in the Harrington, Greenwood and Rising Sun areas. Trap catches totaling 200 or more moths for the month of April generally indicate a potential for outbreaks. You should begin scouting for armyworms by the end of next week or as soon as the heads have emerged.  Examine 5 linear foot of row in 10 locations for armyworm larvae. Armyworms are generally nocturnal, so carefully check for larvae at the base of plants. Since they often cause more damage in barley, the treatment threshold is one per foot of row. In wheat, the treatment threshold is 2 per foot of row.  You should also start looking for sawfly larvae during the next week. Since adults often lay their eggs on field edges and in lodged areas, you should check these areas first for sawfly larvae. A sweep net can be used to detect the first larvae.  Once larvae are detected, sample 5 foot of row innerspace in 5-10 locations in a field to make a treatment decision. You will need to shake the plants to dislodge larvae that feed on the plants during the day. No treatment will be needed until you find 2 larvae per 5 foot of row innerspace or 0.4 larvae per foot of row.

 

In the last newsletter, I included an article written by Galen Dively regarding winter grain mites in orchardgrass.  I have received a few calls about this mite in wheat and if you look closely you will find them in most wheat fields.  At this point, it appears that the warm weather should make the mites inactive; therefore, we do not anticipate the need to treat wheat. However, we will let you know if problems develop. Damage symptoms were observed in wheat in Virginia in January and February. 

 

The following information, provided by Ames Herbert at VPI, provides additional information on winter grain mites and discusses what has been found so far in Virginia:

 

" An infestation of winter grain mite, Penthaleus major (Dugès), was first detected in wheat fields in Chesapeake and Virginia Beach during the months of January and February 2002. Several fields were infested and infestations appeared to be at least somewhat more common in fields that had been previously treated with sludge.  Populations declined to unobservable levels in late February to early March, but re-emerged in early April – indicating a second generation.  The early spring infestations were associated with dead patches where plants began dying in January.  However, we are still not certain that plant death was the result of mite injury, alone, but was associated with additional plant stress caused by a high soil pH condition and manganese deficiency that is common in that area of the state. Discussions with mite experts and perusal of web information have not provided a clear understanding of whether mites are capable of killing large areas of wheat or orchardgrass, what the economic thresholds might be, or what control strategies or acaricides would be most effective.

 

Temperature and moisture are the most important factors influencing mite development and abundance.  Cool, rather than warm temperatures, favor their development.  Egg laying is heaviest between 50° and 60°F; the optimum conditions for hatching are between 44° and 55°F.  When temperatures drop below or rise above these extremes, the mites stop feeding, descend to the ground, or burrow into the soil.  Mite activity in the spring drops rapidly and the eggs fail to hatch when the daily temperature exceeds 75°F.  Aestivating (oversummering resting stage) eggs do not hatch in the fall until rains provide adequate moisture.  On hot, dry days it may be necessary to dig into the soil to a depth of four or five inches to find mites.

 

We are uncertain at this point about which products to recommend for chemical control of winter grain mite.  The available recommendations from other states appear somewhat outdated.  For example, although Di-Syston 8E is listed, it would not be effective.  Dimethoate is labeled, but may not provide good control under cooler temperatures.  Both ethyl and methyl parathion are listed, but these are restricted use products that would require careful use.  We will investigate this further if mite problems persist. More information will be passed along as we learn more about this new and potentially damaging pest. "


 

 

April 5 through April 12, 2002 

Trap Counts Provided by UAP Inc., Seaford, DE and University of Delaware IPM

Location

# Moths

Location

# Moths

Argos Corner

0

Lincoln

-

Bridgeville

12

Little Creek

14

Cheswold

3

Middletown

1

Dagsboro

7

Milford

2

Delmar

0

Milton

1

Georgetown

2

Sandtown

4

Greenwood

3

Seaford

1

Harrington E

1

Selbyville

3

Harrington N

3

Smyrna

-

Kenton

3

Townsend

0

Laurel

0

Wyoming

12

Lewes

0

 

 

 

  


Soil-Applied Herbicides to Emerged Field and Sweet Corn - Mark VanGessel, Extension Weed Specialist;  mjv@udel.edu

 

There are times (like this year) that corn has been planted and is emerged without residual herbicides being applied.  Or to reduce the risk of crop injury, the residual herbicides are applied as the corn begins to emerge.  Most of the soil-applied herbicides can be applied to emerged field and sweet corn.  Only those products containing atrazine will provide control of weeds that have already emerged.  The following is a table for applying residual herbicides to emerged corn with maximum height of corn at time of application.  An * indicates these products contain atrazine.

 

 

Herbicide

Maximum

field corn height

Maximum

sweet corn height

Atrazine

12"

12”

Bladex

no later than 4th visible leaf

do not apply to emerged corn

Princep

do not apply to emerged corn

---

Python

2"

---

Prowl

30” or 8 collars

20-24”

Premixes

 

 

Axiom *

not labeled for emerged corn

---

Basis

no later than 2 collars

---

Bicep II Magnum *

5"

5”

Bullet *

5"

5”

FieldMaster *

not labeled for emerged corn

---

Fultime *

11"

---

Guardsman Max *

12”

12”

Harness Xtra *

11"

---

Hornet

24"

---

LeadOff *

8"

8”

“---“ not labeled for sweet corn

 

 


New Products for Soybeans and Other Crops for 2002 - Mark VanGessel, Extension Weed Specialist;  mjv@udel.edu

 

Soybean

Amplify 84DF (from Monsanto) This is the same as FirstRate from DowAgrosciences.  It is use for postemergence broadleaf weed control, but does have a few weeks of residual control.

 

Boundary 7.8 EC (from Syngenta) When used at 1 pt/A you get:  Dual Magnum 0.83 pt and 4.0 oz Sencor 75 DF.

 

Domain 60 DF (from Bayer) When used at 9oz/A you get:  3.6 oz of Define 60 DF and 4.3 oz Sencor 75 DF.

 

Harmony GT 75DF (DuPont) is a new, more concentrated formulation of Pinnacle 25DF, and its use rate is much less than Pinnacle.  Harmony GT is used at one-twelfth of an ounce per acre.

 

Outlook 6EC (BASF) contains dimethenamid-p which is the more active isomer of dimethenamid (Frontier, Guardsman, and LeadOff).  Since it is more active, the use rates will be lower by approximately 55%.  Outlook controls the same weed spectrum as Frontier; providing good control of annual grasses, some broadleaves and nutsedge.

 

Ultra Blazer 2L (BASF) is a new formulation of Blazer.  The species listed on the label for control is similar between the two formulations.  The level of control is slightly higher with Ultra Blazer, but risk of injury is also slightly greater with Ultra Blazer.  Use rate is 1 to 1.5 pts/A with a non-ionic surfactant.

 

Valor 51WDG (Valent) is a new active ingredient, flumioxazin.  Its mode of action is a cell membrane disruptor similar to Authority and Resource.  It is labeled only for soil applications, it will injury soybeans if applied postemergence.  Soil-applied rates are 2.0 to 3.0 fl oz/A, and rate is a function of weeds present rather than soil type.  Do not mechanically incorporate and do not use with Define, Axiom, Dual, Lasso, or Outlook or else soybean injury may occur.

 

Alfalfa

Raptor 1AS (BASF) has been labeled for alfalfa.  Raptor is very similar to Pursuit with a little more activity.  It can be applied to seedling alfalfa 2nd trifoliate stage or larger or established fields in the fall, spring (dormant or semi-dormant), or between cuttings (before 3 inches of regrowth).  The use rate is 4 to 6 oz/A (NIS/COC + N).  There is a 20 day interval between application and feeding or harvesting.

 

Strategy (UAP) is a pre-packaged mixture of Command plus Curbit.  It is labeled for cucumbers, melons, pumpkins, squash and watermelons.  The label is for post-plant surface application only at rates of 2 to 6 pts/A.  Equivelent rates are:

 

Strategy          Command 3ME          Curbit 3E

2 pts/A             5.3 oz/A                       17 oz/A

3 pts/A             8.0 oz/A                       25 oz/A

4 pts/A             10.6 oz/A                     34 oz/A

 

 


 

Field Crop Diseases -  Bob Mulrooney, Extension Vegetable Pathologist, University of Delaware  bobmul@udel.edu

 

Wheat.

Powdery mildew continues to be seen. Keep monitoring fields. Septoria leafspot caused by Septoria nodorum, was seen for the first time this week, but at a very low level. Keep an eye on the crop especially if wet weather arrives. It needs warm temperatures (68-81°F) and leaf wetness for infection. Without rain epidemics, it does not develop. We also saw a saprophytic fungus, Epicoccum, that produces large dark spores that resemble pycnidia (small black fruiting bodies) of Septoria. The only way to tell them apart is microscopically.

 

 


  

Grain Marketing Highlights - Carl German, Extension Crops Marketing Specialist; clgerman@udel.edu

 

Time to Unload Remaining Old Crop Soybeans

Recent market developments have given an opportunity to those that are holding old crop soybeans to go ahead and make the sale. May '02 soybean futures, currently at $4.71 per bushel, are about 15 cents per bushel higher than they were one week ago. Although soybean demand has continued to be strong in the recent past, this current rally in old crop soybeans is likely to be short lived. Additional reasons for unloading the old crop now are: China continues to be an uncertain market for U.S. soybeans, the Southern Hemisphere is harvesting a very large crop, and if one considers the spread in the futures contracts for the storage months (from May to August), it is duly noted that there isn't any.

 

In terms of marketing strategy for new crop (2002) corn, wheat, and soybeans - prices remain too low to advance sales.

 

 


 

Frost Effects on Winter Wheat - Richard W. Taylor, Extension Agronomist; rtaylor@udel.edu

 

Unfortunately, the following article became lost in the mysterious world of the electronic world wide web ethernet.  Some samples were brought in this past week of USG brand 3209 that showed symptoms consistent with freeze damage as described below.  Many new tillers are growing, but a length of stem two to three nodes long had died on the main tillers.  The leaves above the killed nodes were still alive, but with the warm weather this week, I expect them to die. 

 

Small grains are well in advance of their usual growth stage for this time of the year.  One concern that I have as an agronomist is whether flowering will occur so early this year that we will run a high risk of frost or freeze damage on our small grain crop.  Unfortunately, there’s little we can actually do to prevent this from happening.  We can know the symptoms to expect if conditions occur that might cause frost or freeze damage.  In the following paragraphs, I will review some of the issues, symptoms, and effects possible from frost or freeze damage.

 

Frost or freeze damage can occur from now through heading if three basic conditions are present.  First, the wheat must be in a sensitive growth stage (from Feeke’s growth stage 6 to 11).  Second, air temperatures must drop to a certain critical level.  The third and final condition is that the temperature must remain at the critical level for at least 2 to 3 hours.  Most often we see this occurring on calm, clear nights or in isolated pockets protected from wind by woods or other natural barriers.

 

Wheat tissues are most vulnerable to freezing when in an active state of cell division or cell elongation.  The risk is especially high during stem elongation (Feeke’s growth stage 6 through 9) and heading (Feeke’s growth stage 10.1 and 10.5).  Temperatures in the range of 20 to 24°F can kill segments of the elongating stem or sections of the seed head that are caught in the act of cell division or cell elongation at the time of the freeze.  If this occurs to the main tiller very early in jointing, the younger less advanced tillers will have time to grow and develop and somewhat offset potential yield losses.

 

Wheat leaves can tolerate even colder temperatures, 15 to 20°F, after beginning active growth in the spring depending on the variety and age of the leaves.  The older or more mature leaves are more sensitive to cold than the new or developing leaves.  Seed heads (consisting of spikelets and flowers) can be injured at temperatures as mild as 27 to 29°F.

 

Frost damage to young, developing heads is usually not recognized until after heading is complete, but may have occurred anytime after jointing began (Feeke’s stage 6).  If the growing point is killed before heading then the main stem or tiller will die but may be replaced by the development of a new shoot from the crown of the plant.  Heads damaged by frost are empty and bleached white but the entire head is not always affected.  From boot (Feeke’s stage 10) to early heading, frost damage can affect the entire head, the tip only, the base only, both the tip and the base, or occasionally the middle section only.  Also, empty heads can be caused by a freeze of the elongating internodes during stem elongation (Feeke’s stage 6 to 9).  To identify this latter kind of frost damage, peel back the leaf sheaths to expose the stem internode region.  A damaged internode is evident as a thin, often collapsed, and sometimes brownish section of the stem that is 1 to 3 inches long.

 

Can you make a freeze damage evaluation based on the overall visible symptoms of a field?  No, the visual symptoms can sometimes be misleading since even fields that visibly appear to have minor freeze damage (little leaf burn, good color, plants standing well) can have extensive head and stem damage on closer inspection.  Wait at least 5 to 7 days after the freeze to make a valid assessment.  This allows the temperatures to warm up and active growth to begin again.  In cases where conditions (wheat growth stage and temperatures) were marginal, you may need to wait up to two weeks to make an evaluation.  This will allow enough new growth so you can more easily identify damaged and undamaged plant tissue.

 

To assess head damage when the growing point is still in the boot (surrounded by the leaf sheaths), you will need to either cut into the stem lengthwise to find the growing point or you will have to carefully unroll the leaf tissue that surrounds the growing point.  Examine the tissue and locate the last node or swollen stem section. The head is located just above the uppermost node.  For wheat still early in the reproductive cycle (early jointing), a hand lens may be needed to see the developing wheat head (it will still be very small).

 

An undamaged head will be yellow-green, turgid or firm, glossy in appearance, and plump.  A damaged or killed head is initially white in color but becomes pale white, tan or cream colored later.  It will be limp, dehydrated, have a flatter shape and when compared with undamaged heads it will appear to not be developing in size.  Stem growth will stop if the growing point has been killed.  After two weeks, these stems with killed growing points will be readily visible.  A stem or tiller with a live, developing head will have new green leaf tissue emerged at the top of the stem.  Otherwise, the young growth at the top of the stem will be chlorotic (yellowed) and necrotic (dead/dying) or be absent.

 

To check for stem damage that most often occurs to the lower stem area, remove the lower leaves and leaf sheaths to expose the stem.  Damage symptoms include discoloration, lesions, rotting, splitting, collapsed internodes, and either stem bending or lodging.  The nodes may enlarge and turn a brownish color.  When the lowest most node above the soil level bends to form an elbow shape, the symptom of freeze damage is called bent elbow syndrome.

 

If severe damage occurs to the stem, the disruption in water and nutrient movement can kill the growing point.  Lodging or bending will occur within a few days after a freeze.

 

Less severely damaged stems may not lodge for 2 to 3 weeks.  These stems at first will appear whitish to bleached in color, but turn brownish to a darker discoloration as stems deteriorate.  Often the stem will collapse giving a flatten look.

 

Stems that are only slightly damaged can easily be overlooked.  These plants do not often recover well and the stem will continue to weaken and deteriorate.  Lodging may not occur until near maturity as the head increases in weight.  The continued decline in stem health may cause the head to die or may interfere with translocation of nutrients and water to the developing grain.  To identify these stems, look for small areas of discolored lesions on the internodes or discoloration at the nodes.  Secondary infection with microorganisms can increase the damage.

 

Leaf damage is most likely on lush, rapidly growing wheat.  Leaf damage symptoms are very visible and can be seen shortly after a freeze.  For a severe freeze, leaves show a dark, water-soaked appearance.  When temperatures were marginal, leaves may only show a whitish cast.  Most damaged leaves will become chlorotic (light green to yellow), twisted, crinkled, and necrotic or burned at the tip within a few days.  These symptoms are sometimes confused with nitrogen deficiency symptoms.

 

Leaf damage may slow growth for a short period; but, with warmer temperatures, new leaves will emerge if the growing point is not damaged.  Leaf burn itself has only slight or no effect on yield.  If damage has been extensive at the top of the canopy, new leaves may have difficulty emerging although the new growth should break through the damaged tissue.  Leaves will appear to be crinkled.

 

 


 

Weather Cycles Impact Your Pasture/Hay Fertilization Needs - Richard W. Taylor, Extension Agronomist; rtaylor@udel.edu

 

 

Many areas of the state and region over the past two growing seasons have experienced above normal rainfall that has contributed to excellent yields from many pastures and hay fields.  If you haven’t necessarily paid close attention to your fertility program or recently soil tested your fields, there is a good chance that you’ve drawn down the nutrient reserves in your fields.  Although one does recycle some nutrients in grazing situations, it usually is not evenly spread over the entire pasture, rather recycling is concentrated in those areas near shade or water where animals tend to congregate and rest.  Unlike with corn and soybeans where only a portion of total plant dry matter production is harvested (the grain), hay fields are similar to silage corn where the entire top growth is removed.  This can dramatically increase the nutrient removal rates especially for certain legumes and grasses that take up far in excess of the amount of potassium (K) or potash than they need for maximum growth.  This tendency is called luxury consumption.

 

Alfalfa, red clover, white clover, and other legumes have entered their rapid spring growth phase and many grasses are not far behind.  With the dry fall, winter, and so far early spring, root systems may be smaller than normal and if drought hits during early summer, good root growth encouraged by optimum soil test levels of phosphorus (P) and K will be essential for plants to weather the stress conditions.

 

Over the next several weeks will be an ideal time to scout them for nutritional deficiency symptoms especially if you have not done a soil test recently.  This will be especially critical in legume/grass mixtures.  Many grasses and legumes tend to draw heavily on soil K reserves and will accumulate extra K in the tissue in what is known as luxury consumption.  This rapid draw down of a nutrient essential for maximum legume production can be a critical yield limiting factor.

 

What visual symptoms should you look for when scouting legume fields?  For K, the first visual symptom is usually small, white oblong spots on individual leaflets.  These spots eventually coalesce or blend together to show up as necrosis or dead tissue all around the margin of the leaflet.  The white spots are a classic K deficiency symptom for legumes, especially alfalfa.  For grasses, look for the yellowing along the leaf margins on the older leaves.  Symptoms will progress in toward the mid-rib and can advance to dead ragged leaf edges.

 

If the plants show a general chlorotic or yellow cast to the leaves (especially new leaves) and are generally shorter than normal, the crop is suffering from a sulfur deficiency present or the crop has failed to nodulate [nitrogen (N) deficiency and will be worse on the older leaves].  Nodulation failure is really a N deficiency since the Bradyrhizobia bacteria are not present to fix atmospheric nitrogen in a form usable by the crop.  To decide which it might be, dig up legume plants in several locations and check the roots to see if nodules are present.  If nodules are present on the roots, cut several nodules open and see if they are active.  If active, they should show a reddish or pinkish color on the cut surface of the nodule.

 

Boron is another deficiency that might be present.  Boron deficiency symptoms range from an orangish yellow to a reddish yellow color on the upper terminals.  The internodes are often quite short giving the plant an odd stunted appearance.

 

If you see visual symptoms and can’t pin them down to a particular nutrient deficiency, use either a soil test or a tissue test to confirm a diagnosis of the problem.  Even if you don’t see symptoms, take the time to check your soil test P and K levels and soil pH by soil testing.  With the soil test results available, you’ll know if you need to apply P and K right after the first harvest.

 

 


  

Agricultural Fact –

 

U.S. Agriculture is a $200 billion business.

 

 

 


 

                  Weather Summary

Weeks of April 11 to April 18, 2002

Rainfall:

 0.07 inches: April 12

0.14 inches: April 18

 

Readings taken for the previous 24 hours at 8 a.m.

 

Air Temperature:

Highs Ranged from 93°F on April 17 to 60°F on April 11.

Lows Ranged from 65°F on April 16 to 35°F on April 11.

 

Soil Temperature:

69°F average for the week.

(Soil temperature taken at a 2 inch depth, under sod)

 

Web Address for the U of D Research & Education Center:

http://www.rec.udel.edu

 


 

Compiled and Edited By:

Tracy Wootten

Extension Associate - Vegetable Crops


 Cooperative Extension Education in Agriculture and Home Economics, University of Delaware, Delaware State University and the United States Department of Agriculture cooperating, John C. Nye, Director.  Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914.  It is the policy of the Delaware Cooperative Extension System that no person shall be subjected to discrimination on the grounds of race, sex, disability, age or national origin.

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