Volume 12, Issue 2
April 2, 2004
Volume 12, Issue 2
April 2, 2004
The Weekly Schedule Begins –
This is the first weekly issue for Crop Update in
2004. If you are accessing the
newsletter via the web, please notify me if you encounter problems. Sometimes problems arise that may not affect
the computers on our network here at the
If you received Weekly Crop Update via an email
reminder last year and have not sent me a request for 2004, please do so.
Vegetables
Nitrogen –
To understand why nitrogen is used so widely, it is
important to understand where, how, and why it is utilized by plants. Those of us old enough to remember the
drenching rains of Hurricane Agnes in June, 1972, remember the acres and acres
of pale, yellow knee-high corn in the weeks after the storm. This image brings to focus two
characteristics of nitrogen.
First, it is easily leached from most soil profiles
on Delmarva. After Agnes, nitrogen
fertilizer moved out of the young crops root zone, creating the pale, yellow
appearance rather than the rich, dark green color that bodes well for a good,
healthy, productive plant.
This phenomenon of color relates to chlorophyll,
that amazing molecule that captures the sun’s energy and converts it to sugars,
or a stored energy utilized by the plant for its maintenance and growth. Chlorophyll is a complex molecule, with
nitrogen as a key component. At the risk
of bringing back painful memories from high school chemistry; its molecular
formula is C55H70O5N4Mg. The carbon, hydrogen, and oxygen are obtained
by the plant in the gaseous form from the atmosphere. Nitrogen and Magnesium are the two mineral
constituents of the molecule, and must be obtained from the soil, or in the
case of legumes, the nitrogen is fixed from the atmosphere by Rhizobium
bacteria on the roots.
In short, nitrogen and magnesium are at the core of
the chlorophyll molecule, and in non-legume plants, must be supplied from the
mineral environment of the soil. The
nitrogen component is four-times greater than the magnesium component. A nitrogen deficiency is quickly manifested
in lost production through impaired efficiency of the chlorophyll in the
plant. Of course, nitrogen has other
roles in amino acid and protein synthesis and much more, so any deficiency
results in negative impacts.
While I’ve concentrated on the need for nitrogen,
vegetable growers are very much aware that too much nitrogen, besides being a
waste of money and generating potential negative environmental impacts, can
also hurt crop yield and quality. Hollow
heart on watermelons and potatoes, can be related to excess nitrogen. Too much nitrogen can cause tomatoes to be
“viney” and delay maturity. Many
vegetable crops will experience delayed maturity if nitrogen applications are
too high.
Nitrogen recommendations from the University’s and
most commercial labs are based on research and field experience. They are just that, a recommendation, not a
prescription. Each grower does have, and
must have, some flexibility to tailor those recommendations for conditions in
his field and farm. Quite often I
encountered a grower who used ten percent more, or ten percent less than the
recommendation. They have a logic and
rationale for those decisions that are farm-based and cost-driven.
Pea Planting.
Progress in pea planting as of March 30 is about
25-30% of the total intended plantings.
Earliest plantings are up and look good.
Although the weather has been cool, the lack of wet weather has allowed
plantings to proceed fairly well.
Typically, about 8,000 acres of peas are planted. Four processing companies contract with
PictSweet Frozen Foods Obtains Former Agri-Link
Plant in Bridgeville.
PictSweet Frozen Foods has obtained the former
Agri-Link Plant in Bridgeville.
PictSweet has done business in
Vegetable Diseases - Bob Mulrooney, Extension Plant
Pathologist, bobmul@udel.edu
Peas.
Be sure to rotate pea planting 4-5 years to avoid
and reduce root rot. Ridomil Gold 4E
applications broadcast after planting can be useful if Pythium control is
needed. Avoid compacted, poorly drained fields when planting peas to avoid root
rots.
Spinach.
Be sure to check overwintered fields for white rust. As soon as white rust is
seen or discovered in the area, apply Quadris as a foliar spray on susceptible
varieties.
Field Crop Insects - Joanne
Whalen, Extension IPM Specialist;
jwhalen@udel.edu
Alfalfa.
Lower weevil
populations in 2003 in combination with colder winter temperatures may result in
lower populations this spring. However, you should still
begin sampling fields for early feeding signs. We can now find low levels
of larvae in alfalfa in
Field Corn.
We will again be
cooperating with UAP Inc. in a pheromone trapping program for
black cutworm moths. The first moth was caught last week in Leipsic. Although no precise numbers are available,
moth catches of 9 to 15 moths per 7-day period have been associated with a
moderate to high potential for cutworm outbreaks. Larvae will be large
enough to begin cutting when about 300 base-50 degree-days have accumulated
since peak moth activity and egg laying. By
calculating cutworm hatch and development over time, we can anticipate when to
look for damage. Pheromone trap catches help us determine when peak moth flight and egg laying occurs; however, they cannot
predict the amount or magnitude of cutting that will occur. The presence of a
major flight only means that the potential for an outbreak exists. Adverse
weather, lack of adequate food for newly hatched larvae, predation, and disease
can reduce larval populations. You can use pheromone trap and degree-day
information to estimate or predict when first cutting will occur. Scouting of
seedling corn near the first cutting date is the best way to determine whether
a problem exists. Just a reminder, if you plan to tank mix a pyrethroid with a herbicide for
cutworm control, it should be done at or immediately following planting. Pyrethroids combined with early burn-down applications, 2-3
weeks before planting, have not provided effective control.
Just
a reminder, the lowest labeled rate of Poncho 600 on field corn is 0.25 mg
ai/kernel (Poncho 250) and the lowest labeled rate of Cruiser is 0.125
mg/kernel. No data is available for the
use of lower than labeled rates. Since a high percentage of corn seed has been
treated with Cruiser or Poncho this season, remember that these two products
have not provided bird repellency. If you are in an area where birds have been
a problem, you should consider using a hopper box treatment that has lindane in
the mix. Based on grower and personal
experience, the use of hopper box treatments containing lindane have helped
with bird repellency. In addition, depth of planting has a large impact on the
amount of bird damage you will see. Remember, birds pull corn out of the ground
to feed on the seed. If you anticipate a bird problem, you should avoid shallow
planting and plant corn 1 ¾ to 2 inches deep. This will to reduce their ability
to pull corn out of the ground. However, be sure to watch your seed depth
carefully when planting 1 ¾ inches and deeper, especially in sandy soils, to
avoid emergence problems.
Timothy.
Reports from around the region indicate that cereal rust mites
can now be found in timothy. As soon as fields green up, you should begin
checking for mites and the early signs of infested leaves, especially in fields
with problems in past years. These mites
are microscopic, so the use of a 20x-magnifying lens is necessary. If rust
mites become a problem , Sevin XLR Plus still has a
24C registration on timothy for rust mite management. The following are the use
directions for this label: Apply 3 pts per acre (1.5 pounds ai
per acre) using ground equipment only with adequate water for complete coverage
(20 or more gallons by ground). One application should provide enough
suppression to prevent economic yield and quality losses. Apply at
approximately 3-4 weeks after green-up in fields with a previous history of
rust mites and/or when 25% of the plant tillers exhibit curled tips of the new
leaf blades. It has a 30 day wait until harvest.
Wheat.
Although we are starting to find fields with symptoms of barley
yellow dwarf virus (BYDV), it still appears that the most important time to
control aphids and help reduce problems from BYDV is the first 30 to 60 days
after plant emergence. Although it is possible to have virus vectored in
the spring, if you see BYDV in wheat this spring it was likely vectored late
last fall and early winter. Information from
Be sure to begin sampling fields by mid-April for
cereal leaf beetle activity. Since a number of fields experienced economic
levels in 2003 and we are finding the first evidence of adult feeding, fields
should be scouted early for the presence of egg masses. In recent years, the
threshold for cereal leaf beetle has been adjusted to include sampling for
eggs, especially in high management wheat fields or areas where problems were
experienced the previous year. The eggs
are elliptical, about 1/32 inch long, orange to yellow in color when first laid
changing to a burnt orange prior to hatching. Check our website for pictures of
cereal leaf beetle adults, larvae and eggs
(http://www.udel.edu/IPM/facts/clbpictures.htm) Generally,
eggs are laid singly or in small scattered groups (end-to-end) on the upper
leaf surface and parallel to the leaf veins. Cereal leaf beetle larvae are
brown to black, range in size from 1/32 to 1/4 inch long, and eat streaks of
tissue from the upper leaf surface. Since cereal leaf beetle populations are
often unevenly distributed within the field, it is important to carefully
sample fields so that you do not over or under estimate a potential problem.
Eggs and small larvae should be sampled by examining 10 tillers from 10 evenly
spaced locations in the field while avoiding field edges. This will result in
100 tillers (stems) per field being examined. Eggs and larvae may be found on
leaves near the ground so careful examination is critical. You can also check
stems at random while walking through a major portion of the field and sampling
100 stems. The treatment threshold is 25 or more eggs and/or small larvae per
100 tillers. If you are using this
threshold, it is critical that you wait until at least 50 – 60% are in the larval stage (i.e. after 50% egg hatch). If the
egg/larvae threshold is not used, the threshold of 0.5 larvae per stem can
provide enough lead-time to provide good control if fields are scouted
carefully and fields are visited twice a week when populations are approaching
threshold levels. Sevin
will provide good control of cereal leaf beetles although past experience
demonstrated that it could result in aphid explosions by reducing predator
populations. Furadan provides good control; however,
it cannot be applied once grain is heading. Lannate,
Mustang MAX and Warrior will provide good control of the entire insect complex
present in small grains (cereal leaf beetles, aphids, armyworm
and grass sawfly). Two years of research data from Ames Herbert in VA indicates
that Warrior has provided longer residual control if applications are made
based on the egg threshold. However, if applications are made when larvae are
the predominant stage, all products have provided similar levels of control. Neither Mustang MAX nor Warrior are labeled on barley at
this time.
Field Crop Diseases - Bob
Mulrooney, Extension Plant Pathologist, bobmul@udel.edu
Wheat.
We are getting samples of wheat plants already from
irregular spots in the fields that have a mottled yellow appearance. This could
be barley yellow dwarf, but the samples have been sent for virus identification
and confirmation and we will be keeping you updated as the season progresses.
Barley yellow dwarf is transmitted by aphids either in the fall or spring. It
is generally fall infections that cause the most yield loss. Other virus
diseases of wheat include wheat spindle streak and wheat soil born mosaic
virus. These two viruses are soil born because they are transmitted by fungi
that have the virus and transmit the virus when they infect the wheat roots in
the fall. All three viruses can produce irregular patches of yellow stunted
wheat in the early spring. The soil born viruses will be worse in low areas of
the field in contrast to barley yellow dwarf infections which are random. Wheat
soil born mosaic almost always will be found in the low spots of the field.
There is no control for the viruses once they appear. The soil born viruses can
be controlled in the future by planting resistant wheat varieties. Researchers in
Soybean
Cyst Nematodes.
It is not too late to soil test for the soybean
cyst nematode (SCN). If soybean stubble is present, sample with a soil probe
6-8 inches deep between the plants in the row.
Samples should be taken before any spring tillage. Sample size should be
20-25 cores taken in a zig-zag pattern across the field. Ideally samples should
represent no more than 10-20 acres. Sample bags and information sheets are
available from the county extension offices. The cost is $10 per sample. New
fields and those to be planted with susceptible varieties are the most critical
to sample at this time.
Keep in mind, that most Roundup Ready varieties do
not have resistance to race 1 of the soybean cyst nematode (SCN) but carry some
resistance. This makes monitoring SCN
populations more important if you are growing continuous soybeans and using
Roundup Ready varieties. Periodic sampling can indicate if SCN populations are
increasing. Soybean variety trial results are available from the
Herbicide/Insecticide
Reminders -
Counter, Lorsban, and Fortress are organophosphate (OP) insecticides used in this area. Many of the postemergence herbicides have precautions about applying them to corn previously treated with OP insecticides. Herbicides that list restrictions or precautions include Python, Hornet, Accent, Basis Gold, Steadfast, Steadfast ATZ, Celebrity Plus, Harmony GT, Pinnacle, Beacon, Exceed, NorthStar, Spirit, Callisto, Option, Equip, and Lightning.
If you are considering
using any of these herbicides, refer to the label regarding restrictions /
precautions with OP insecticides before you plant.
Section 18 for Sinbar in Watermelons -
The State of
Reminders on Acetochlor Use
Restrictions -
Acetochlor is a
preemergence herbicide for corn that controls annual grasses and some broadleaf
weeds. It is in the following products:
Harness, Harness Extra, Degree, Degree Extra, Topnotch, Fultime, and
Keystone. There are restrictions that
are important in our area. The
restrictions pertain to groundwater quality.
The restrictions are based on depth of groundwater within one month of
planting and the combination of soil type and organic matter. Do not apply acetochlor if the groundwater
depth is within 30 feet and you have
sands with less than 3% organic matter, loamy sands with less than 2% organic
matter, or sandy loam with less than 1% organic matter.
New(er) Corn Products for 2004 -
Some of these products were available in 2003.
Equip
32WDG (Bayer) is a premix of Option (foramsulfuron) and
a new ALS-inhibiting herbicide called iodosulfuron. (Iodosulfuron is not available in any other
herbicide at this point.) In addition to
the two herbicides, it contains a crop safener.
It is for postemergence use at a rate of 1.5 oz/A. The label requires that it be applied with
MSO and nitrogen. Equip can be applied
over the top of corn up to 12 inches tall (or V4 stage) and from 12 to 36 inches
(or V4 o V8 stage) with drop nozzles.
There are numerous grasses and broadleaves listed as controlled on the
label. There are precautions about use
for corn previously treated with Counter or Lorsban, refer to label. There is no problem with planting small
grains in the fall, but there are a number of vegetable crops that are listed
as 18 month plant back intervals.
Keystone 5.25 SE
(DowAgroSciences) is a premix of acetochlor plus atrazine. This is a new formulation of acetochlor and
atrazine to improve handling and suspension.
There are the same restrictions for groundwater concerns as all other
acetochlor formulations. There is also a
formulation called Keystone LA for
situations where lower atrazine is needed.
Lumax
(Syngenta) was available last year.
There were some mixing problems with liquid fertilizer and now Syngenta
recommends a compatibility agent with
phosphate ester when using suspension or liquid fertilizers with N-P-K-S as the
carrier. There were also a few
cases when after the tank was mixed, the products were allowed to settle out
and it was difficult to resuspend the mixture.
Syngenta developed some guidelines for situations if the spray solution sits for over two hours
without agitation. It is recommended to
use clay suspension agents (Attagel 50 or Min-U-Gel 200) if water is the
carrier. Unfortunately, these clay
suspension agents will deactivate paraquat and glyphosate products and may
require separate application for paraquat and glyphosate to control weeds that
have emerged. Syngenta is developing a
new formulation of Lumax to overcome these problems.
Steadfast 75WDG (DuPont) is a pre-packaged mixture of Matrix and Accent. It was available in 2003. It is a postemergence herbicide with a use rate of 0.75 oz/A. This use rate is equivalent to 0.75 oz/A Matrix plus 0.5 oz/A Accent. This is a higher rate of Accent than what is in Basis Gold. There are precautions with organophosphate insecticides, refer to label.
Steadfast
ATZ 89.3 WDG contains atrazine.
It is the equivalent of 0.75 oz/A of Steadfast, but with 0.75 lbs of
atrazine.
Prowl
H2O 3.8AS (BASF) is new
pendimethalin formulation. Same uses as
Prowl and other formulations of pendimethalin, only it is a water-based
formulation, and the use-rate structure is different from the 3.3EC
formulation. The new formulation makes
the product more user-friendly. The
pendimethalin (active ingredient) is inside capsules that rupture through
wet/dry cycles of the soil. Planting
precautions with corn remain the same to prevent root pruning of the corn
plants.
Dicamba Formulations for Horseweed
Control -
There has been some
confusion about use of Clarity and/or Banvel for weed control prior to planting
soybeans. Both Clarity and Banvel
contain only dicamba as the active ingredient and both are labeled prior to
planting soybeans. Both require a period
of time between application and planting.
Banvel restriction is 30 days
regardless of rate. The Clarity label requires a cumulative
amount of rain or irrigation of 1 inch (meaning the rain does not have to fall
all at one time) followed by 14 days before planting if less than 8 oz of
product is used (longer interval is required if more than 8 oz/A is used).
Preemergence Herbicide Rates in Corn -
I have been asked about
comparable rates of various premixed soil-applied herbicides for corn. That is very difficult to come up with. All of these pre-mixes have varying ratios of
atrazine and chloroacetamide herbicides.
Chloroacetamide herbicides are the grass herbicides such as metolachlor
(Dual) or acetachlor (Harness), or dimethenamid-p (Outlook). Some of the basic manufacturers in our area
encourage the use of their products at rates above what is recommended on the
label to ensure consistent performance.
I have told people when they ask about comparable rates, that you have
to look at the label and see what the companies themselves recommend for a
given soil type and organic matter content.
The soils in our region (high percentage of sand and low organic matter)
are not well suited to hold enough herbicide for full-season weed control. Unless we have ideal conditions that allow
for early activation of the herbicide and excellent growing conditions for
vigorous corn growth immediately after planting, the soil-applied herbicides
are not likely to provide season-long weed control and will need some
postemergence herbicides to keep the fields clean until harvest.
There have been changes in formulation and ratios of products for many pre-packaged herbicides over the past few years. As a result, check the label for your product of choice since often the new formulations recommend lower use rates than what was previously labeled.