Vegetables

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

 

Melons.

Continue to scout all early-planted melons for aphids, cucumber beetles, and spider mites. The threshold for mites is a 20- 30% infested crown with 1-2 mites per leaf. If populations of mites explode and adult mites are the predominant life stage, Capture or Danitol should be used. If the population is a mixture of eggs, immature mites and lower levels of adult mites, Agri-Mek should be used at 8 oz/acre. A second miticide application may be needed in 3-7 days depending on the population level at treatment time. In general, dimethoate has provided very poor mite control. The treatment threshold for aphids is 20% infested plants with at least 5 aphids per leaf. Fulfill, Lannate and Thiodan are labeled on melons and will provide melon aphid control. Dimethoate will not control melon aphids.

 

Peas.

As the earliest peas bloom and set pin pods, be sure to sample for aphids. Although levels have been generally low, we are starting to see an increase in populations. The warmer weather could result in a rapid increase in populations. 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.

 

Potatoes.

The first Colorado potato beetle adults and egg masses have been found in the earliest emerged fields. Actara, cryolite, Spintor or Provado will provide control. To avoid the development of resistance to Actara or Provado, fields treated with Admire, Platinum or Tops MZ Gaucho at planting should not receive foliar treatments of Provado or Actara. Corn borer counts remain below one per night except in the Bridgeville, Greenwood, Laurel and Seaford areas where catches are at one per night. Be sure to check our website (http://www.udel.edu/IPM/traps/latestblt.html) for the most recent moth catches in your area. In general, we tend to see an increase in moth populations as soon as temperatures increase after a period of cool rainy weather.

 

Sweet Corn.

Be sure to watch fields planted under plastic for European corn borer larvae.  A treatment should be applied if 15% of the plants are infested. The best timing for a treatment is just as the tassels are emerging from the whorls. In recent years, Baythroid, Mustang, Penncap or Warrior have provided effective control. You should also continue to watch for black cutworm and flea beetle activity. Damage from both insect pests has been observed in early-planted sweet corn.

 

 

 

Sinbar Receives Section 18 Label for Watermelons – Ed Kee, Extension Vegetable Crops Specialist; kee@udel.edu

 

The EPA has approved Sinbar for preemergence use on watermelons at the rate of 3 to 4 ounces per acre.  Sinbar has become an important weed control tool since it received its first Section 18 approval several years ago.

 

 

 

Pickling Cucumber Weed Control – Ed Kee, Extension Vegetable Crops Specialist; kee@udel.edu

 

Planting for pickling cucumbers began last week on the Eastern Shore of Maryland and in Delaware.  Curbit and Command can be considered as an effective standard treatment for preemergence use.  On the earliest plantings, we recommend 1.5 pints/acre of Curbit and 4 ounces/acre of Command.  When the soil is warmer, there is merit in increasing the rate of Curbit to 2 pints per acre to improve broadleaf weed control when there is less risk of crop stunting as the weather warms.

 

Strategy is a jug-mix of Curbit and Command.  1.5 pints of Strategy delivers 1 pint of Curbit and 4 ounces of Command.  We would recommend adding ½ pint of Curbit to the mix, if Strategy is used.  One pint should be added as the weather warms to reflect the same recommendation stated above.

 

Sandea is also available for preemergence and post emergence treatments.  It is especially useful for nutsedge and other broadleaf weeds.  The rate in either case is 0.5 to 0.66 ounces per acre.  Read the label and the Commercial Vegetable Recommendation Guide for further details on timing, use of surfactants and other important information.  Do not use if organphosphate insecticides have been applied to the crop.  Check the label for plant back or carry-over restrictions for subsequent plantings.

 

Select 2EC and Poast 1.5 EC are also labeled for post-emergence grass control.  Again read the label for complete directions.

 

Mechanical cultivation is still an important component of a pickle weed control program.  If the tractor-mounted harvesters will be used, it is important to minimize soil ridging from the cultivator operation.  The ridges prevent the harvester pick-up reel from getting low enough to gather all pickles.

 

 

Sandea On Melons - Mark VanGessel, Extension Weed Specialist;  mjv@udel.edu

 

Gowan has a label for Sandea use on watermelons and cantaloupes.  However, the label is not the same for both.  The use pattern on watermelons is row middles only at 0.5 to 1 oz/A.  For cantaloupes, the use pattern is preemergence for direct seeded melons only.  Postemergence applications can be made post-transplant only to bare-ground (not for melons grown on plastic).  Sandea does have a label for pre-plant under plastic, with at least a 7-day interval between application and transplanting.  (I personally do not have experience with this use.)  Finally, Sandea can be used on row middles of cantaloupes.

 

 

 

Vegetable Crop Diseases - Bob Mulrooney, Extension Plant Pathologist, bobmul@udel.edu

 

Snap beans.

Apply Ridomil Gold 4E or UltraFlourish in a 6 in. band over the row at planting to control damping-off caused by Pythium. If Pythium and Rhizoctonia are a problem apply Ridomil PC 11G at planting.

Research work last season on lima beans demonstrated improved stands from Rhizoctonia control if lima beans were treated with Maxim seed treatment at the 0.08 fl. oz/cwt. rate. The implication is that the same would be true for snap beans.

 

 

Field Crops

 

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

 

Alfalfa.

Continue to sample fields for alfalfa weevil. In general, populations are low throughout the state and early cutting should be the best control option for most fields. If you were approaching economic levels before cutting, you should sample for weevil larvae and adults within one week of cutting. In recent years, we have found adults causing as much damage as larvae. No treatment should be needed after the first cutting unless you can find 2 larvae and/or adults per crown and they are feeding on the regrowth.

 

Field Corn.

Black cutworm moth activity and egg laying significantly increased throughout the state this past week (http://www.udel.edu/IPM/traps/currentbcwtrap.html). Be sure to watch for cutworms feeding above and below ground. We have had reports of cutworms feeding below the soil surface. Although we did not get a positive identification on the species, the size of the worm indicates that it may have been variegated cutworm. The early signs of leaf feeding and occasional cut plant from small black cutworms indicates that cutting is happening earlier than the degree-day model predicted, so be sure to watch fields carefully.  A treatment in 1-2 leaf stage should be applied if you find 3% cut plants or 10% leaf feeding. The threshold in 3-4 leaf stage corn increases to 5% cut plants.  A pyrethroid or Lorsban will provide the best control. Fields should be scouted through the 5^th leaf stage for cutworm damage. If cutworms are feeding below the soil surface, it will be important to treat as late in the day as possible, direct sprays to the base of the plants and use at least 30 gallons of water per acre. We are also seeing bird damage in early emerging corn. Although birds can cut plants off at the soil surface, they tend to pull plants out of the ground. In addition, if you look closely you will see "bird prints" near the missing plants, so do not confuse it with cutworm damage. In general, birds will pull plants out of the ground instead of cutting.

 

Small Grains.

Economic levels of cereal leaf beetle larvae can be found in spots throughout the state, so continue sampling for larvae. At this time, the treatment threshold is 0.5 larvae per stem  (flag leaf and next 2 stem leaves) and 10% defoliation. Lannate, Mustang or Warrior will provide effective control. Lannate is labeled on barley and wheat.  Mustang and Warrior are only labeled on wheat. Aphid populations have also increased in some areas so fields should be sampled for aphids as heads emerge.  Although lady beetle populations can keep aphid populations in check, cooler weather followed by quick warm up will allow aphids to increase, but beneficials often lag behind. All barley and any early wheat in head should be sampled for aphids. The treatment threshold is 20-25 per head with low beneficial activity (less than 1 per 50 aphids). Continue to sample barley and wheat for armyworm and sawfly larvae. We have found the first small armyworm and sawfly larvae in wheat in Sussex County. Although armyworm moth counts still remain low, we could see later activity this year.

 

Soybeans.

As you plan to plant your first no-till full season beans, be sure to consider a treatment for seed corn maggot. In no-till fields, seed corn maggot will remain a problem through May. Flies continue to lay eggs and maggots will be present at the time of seed germination. Kernel Guard Supreme and KickStart VP are both labeled on soybeans.  The active ingredient in both products is permethrin.

 

 

 

Field Crop Diseases - Bob Mulrooney, Extension Plant Pathologist, bobmul@udel.edu

 

Wheat.

Powdery mildew is still the most prevalent disease on susceptible varieties. Disease pressure is increasing, so check fields regularly especially once the flag leaf emerges. Be aware that some of the newer varieties have levels of resistance that express themselves by producing a few powdery mildew lesions or spots throughout the canopy, but the level of infection remains low. These are hard to judge whether or not to apply a fungicide, but if you check the disease reactions from our variety trials you may get an idea of the varieties reaction here.

 

I have seen several samples of a tan, zonate spot only on the upper leaves of wheat in both Sussex and New Castle counties. They are not numerous (maybe 1-2/leaf), but look like a fungus disease. As of this writing, I believe they are some type of physiological spotting or environmental. Isolations have not produced a pathogenic fungus although some of the spots are colonized by fungi that live on dead tissue like Cladosporium, which causes sooty mold later on heads that are damaged by drought, freezing, or other problems.

 

The spot blotch form of net blotch continues to be found on susceptible barley cultivars. This disease produces oval, reddish-purple spots on the leaves.

 

* Please note-Correction

In the April 25^th, Issue 5 of Weekly Crop Update, I reprinted an article on wheat fungicides from Don Hershman in Kentucky which included this statement: “In contrast, Tilt (propiconazole), and Stratego, which contains propiconazole, must be applied to the crop before 50% crop flag leaf emergence”.

This is not true for Delaware and Maryland, Tilt has a 24-C label that allows for application up to head emergence. I am sorry that I did not catch this statement before I submitted it for the newsletter and for any confusion it may have caused our readers.

 

Alfalfa.

Spring black stem can be a problem for Delaware growers. Look for dark brown to black lesions on the stem that can be several inches long, and coalesce to cover most of the stem when severe. Infections can also occur on leaflets. Typically these appear as small dark brown to black spots; just a few of these can cause the leaflets to turn yellow and fall off. If the disease continues to develop, cut and bale the growth early if possible. Even if you normally wait until early flowering, a severe outbreak of spring black stem can justify cutting during the bud stage. By leaving the crop in place, it will continue to defoliate (costing a producer loss in yield and in forage quality). By cutting early, producers will capture whatever yield is available, and it will allow sunlight and wind movement to penetrate to the new crown buds that will break dormancy when the disease gets severe enough.

 

The recommendation is to cut alfalfa when it is ready, not to wait for a forecast of 3-4 days of sunny, dry conditions. Advancing maturity causes substantial loss of forage quality anyway, and this would only be made worse if spring black stem is active. Thus, waiting for dry weather can cost as much or more than rain damage to the hay.

 

 

 

Where Does the Lime Go? - Richard W. Taylor, Extension Agronomist; rtaylor@udel.edu

 

Thanks to an invitation from one of the area’s crop consultants, I got to visit a wheat field in Sussex County today that is showing unusual patterns, but thanks to tissue and soil test results we at least understand what the problem is if not the underlying cause.  The soil pH results indicated a pH of 5.9 in the good areas and 5.1 in the bad areas and more importantly showed that both calcium (Ca) and magnesium (Mg) base saturations were well below recommended levels despite the field having received a substantial application of wet lime (Hi-Mag lime as well) in the past year.  Tissue tests indicated all nutrients were adequate except for Mg that was right at the critical (deficient) level.

 

If you examine Photos 1, 2, and 3, you can see potential soil patterns (bottoms of hills greener—possibly from higher cation exchange capacity) (Photo 1), possible equipment-made patterns in Photo 2, and a yellowing stripe that follows the lane and then moves out into the field where an irrigation well is located (Photo 3). 

 

Photo 1.  Field wide view of Mg deficiency patterns in a wheat field that had received about 1.5 tons/A wet lime in the past year and manure about two years ago (Photo by R. Taylor).

 

Photo 2.  Closer view of man-made pattern of Mg deficiency in a wheat field that had received about 1.5 tons/A wet lime in the past year and manure about two years ago (Photo by R. Taylor).

 

Photo 3.  Field wide view showing stripping patterns in a wheat field that had received about 1.5 tons/A wet lime in the past year and manure about two years ago (Photo by R. Taylor).

 

The wheat was very close to heading out being in the late boot stage of growth and normally you might not consider any rescue treatment because much of the yield potential has been determined.  In this case with fertigation possible using the center pivot system in the field, the consultant and I were recommending the use of Po-Mag (potassium magnesium sulfate) that can be applied in a light irrigation and quickly, we think, green up the plant.  Many of the lower leaves were turning yellow as the Mg is mobilized by the plant and sent to the growing point and flag leaf.  The treatment should be relatively inexpensive to apply requiring only a small increase in yield to make the treatment cost effective.  The additional chlorophyll produced when Mg is applied should lead to that much yield increase even at this late stage of growth.

 

Dual Injury on Corn - Richard W. Taylor, Extension Agronomist; rtaylor@udel.edu; Greg Binford, Assistant Professor,University of Delaware, binfordg@udel.edu

 

The unusually hot and cold spring weather is beginning to cause interesting symptoms to show up in some corn fields.  Photo’s 1 through 3 show classic acetanilide injury symptoms on corn planted in a conventional seedbed when soil was very moist.  The corn also received in-furrow fertilization with 2.0-2.1 gal/A* of 8-20-0 (plus the labeled rate of Regent) and a 2 X 2 banded fertilizer application of 12 gal/A of an 8-20-5.  The herbicide treatment was a preemergence application of 5 pt/A of Lumax that provides a higher rate of safened Dual than is normally used with Bicep.  Lumax at 5 pt/A provides 1.76 pt of Dual while Bicep II Magnum at 2 qt/A provides 1.25 pt/A of Dual.  The very moist conditions and the little bit of rain received since planting may have been adequate to activate the Dual which is very water soluble.

 

* We were informed the true rate of in-furrow fertilization was 2.0-2.1 gal./A instead of the 2.5 gal./A previously stated.  We apologize for the inaccuracy.

 

Photo 1.  Affected corn seedlings from field treated with 5 pt/A Lumax and both pop-up and banded starter fertilizer (Photo by G. Binford).

 

Photo 2.  Corn seedlings that had leafed out underground (Photo by R. Taylor).

 

Photo 3.  Injured corn seedlings from field showing no crusting but treated with 5 pt/A Lumax and both pop-up and banded starter fertilizer (Photo by R. Taylor).

 

The unusual weather and other conditions may have contributed to this field problem.  The stand appears to have been reduced by about 10 to 15 percent from the number of seed planted per acre, but after calculating in the expected germination percentage the number of affected seedlings is closer to 5 to 10 percent.  This particular stand was still adequate for near maximum yields.

 

These symptoms are similar for all chloroacetamide herbicides (Dual, Lasso, Outlook, and Harness).  Cool, wet soils increase the likelihood of injury.  Soil crusting and insect damage can also cause this type of symptom as well.

 

Consultants should closely observe fields for the above symptoms and especially those fields with light sandy soil with low organic matter levels if they have been treated with Lumax.  Please pass along your observations to Dr. Mark VanGessel at the University of Delaware, or Dr. Ron Ritter at the University of Maryland.