Volume 12, Issue 12
June 11, 2004
Vegetables
Vegetable Crop Insects -
Cucumbers.
Continue
to scout for cucumber beetles and aphids. Fresh market
cucumbers are susceptible to bacterial wilt, so treatments should be applied
before beetles feed extensively on cotyledons and first true leaves. Pickling
cucumbers have more tolerance to wilt, but a treatment may be needed if you
find 2 or more beetles per plant and significant damage can be found on the
cotyledons. A treatment should be applied for aphids if 10 to 20 percent of the
plants are infested with aphids with 5 or more aphids per leaf. Fulfill, Thionex or
Lannate will provide aphid control. Be sure to watch
for bees foraging in the area and avoid insecticide applications on blooming
crops. A pyrethroid, Lannate, Sevin or Thionex are labeled for cucumber
beetle control in cucumbers.
Melons.
Continue to scout all melons for aphids, cucumber beetles, and spider
mites. If spider mite populations are high at the time of treatment, 2 sprays
spaced 5 days apart may be needed. The threshold for mites is 20-30 percent
infested crowns with 1-2 mites per leaf. Acramite, Capture, Danitol,
Agri-Mek or Kelthane will
provide control, but should be rotated to avoid the development of resistance.
The treatment threshold for aphids is 20 percent infested plants with at least
5 aphids per leaf. Continue to watch
fields carefully for cucumber beetles. Be sure to look under the plastic where
beetles can often hide until disturbed. Be sure to watch for bees foraging in
the area and avoid insecticide applications on blooming crops.
Peppers.
In
areas where corn borer trap catches are above 2 per
night and pepper fruit is ½ inch in size or larger, fields should be sprayed on
a 7-10 day schedule for corn borer control.
If fruit is not present, larvae hatching from egg masses will feed on
the leaves then move into the petioles and stems. For these fields, a pyrethroid application should be considered especially if
egg masses are found and trap catches are above 10 per night in your area.
Correction to the Vegetable Recommendations for Acephate(Orthene) on Peppers.
If you read the current Orthene 75S label (as well as all current
acephate labels), European corn borer control (ECB) is only listed under bell
peppers and the rate is 1-1.33 lb per acre of Orthene 75S (not 0.67-1.33 as
listed in the book). After talking to Valent, it appears that ECB was
mistakenly dropped from the non-bell pepper label. The current label states aphid control only at a rate of
0.67 lb/acre.(Orthene 75S). Another
difference is the maximum amount allowed on each pepper type (bell versus
non-bell). Regardless of the formulation (Orthene 97, Orthene 75S or generic
acephate), the maximum amount allowed for bell peppers is 2 lb ai/a/season. On
non-bell peppers the maximum amount is 1 lb ai/a/season. Valent Corporation (
manufacturer of Orthene 97) has agreed to submit a 2ee label to EPA for DE,MD,
NJ, PA, and VA to add corn borer back on the Orthene 97 label for non-bell
peppers at a rate of ¾ - l lb per acre.
With this label change, you will be limited to one Orthene (acephate) application
for corn borer control on non-bell peppers.
We will let you know when we receive the 2ee label.
Potatoes.
Continue to scout fields on a weekly basis for Colorado potato beetle (CPB) adults and larvae. The treatment threshold for
adults is 25 beetles per 50 plants and defoliation has reached the 10 percent
level. The larval threshold is 4 small larvae per plant or 1.5 large larvae per
plant. The threshold for each should be reduced by 1/3 to 1/2 if all stages are
present. Avaunt + PBO, Actara, cryolite, Spintor or Provado will provide control. Economic levels of potato
leafhopper adults and nymphs can be found in many fields. As a general
guideline, controls should be applied if you find ½ to one adult per sweep
and/or one nymph per every 10 leaves. Dimethoate, a pyrethroid, Actara or Provado will provide
control.
Snap Beans.
All fields should be scouted for leafhopper and thrips activity, especially seedling stage beans. The thrips threshold is 5-6 per leaflet and the leafhopper
threshold is 5 per sweep. If both insects are present, the threshold for each
should be reduced by 1/3. Dimethoate, Lannate, Asana, Capture, or Warrior will provide control of
both insect pests. Once corn borer catches reach 2 per night, fresh market and
processing snap beans in the bud to pin stages should be sprayed for corn
borer. Acephate
should be used at the bud and pin stages on processing beans. Once pins
are present on fresh market snap beans and trap catches are above 2 per night,
a 7-10 day schedule should be maintained for corn borer control. Lannate, Asana, Capture, Warrior or Mustang are labeled. Acephate has a
14-day wait until harvest. Be sure to check our website (http://www.udel.edu/IPM/traps/latestblt.html)
for the most recent moth catches in your area.
Sweet Corn.
All silking sweet corn should be sprayed on a 4-5
day schedule.
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Vegetable Crop Diseases
-
Belly Rot on Pickling Cucumbers.
This fungus disease of the fruit is an often frustrating disease to prevent.
The causal fungus Rhizoctonia solani
is very common and can remain viable in the soil for many years. It has a very
large host range and rotations are not very effective in control of
Rhizoctonia. The optimum temperature for infection is 81°F and high humidity
under dense foliage also contributes to favorable conditions for fruit
infection. Rotations away from cucurbits can help as well as deep plowing
before planting to bury the fungus. The most favorable conditions for belly rot
are usually in July and early August following an early crop of pickles.
Unfortunately fungicide control has always been inconsistent. The only labeled
control is applications of Quadris or Amistar at the four leaf stage and again
at flop or vine tip-over. This application timing requires another application
in addition to any fungicide sprays for Phytophthora fruit rot control. (See
last weeks newsletter for info on Phytophthora fruit rot control.)
Potato Disease Advisory.
Disease Severity Value
(DSV) Accumulation as of June 9, 2004 is as follows:
|
Date |
Daily DSV |
Total DSV |
Spray Recommendation |
|
4/25- 5/18 |
4 |
18 |
7-day |
|
5/19 |
4 |
22 |
7-day |
|
5/20 |
2 |
24 |
7-day |
|
5/21 |
2 |
26 |
7-day |
|
5/25 |
5 |
31 |
7-day |
|
5/27 |
3 |
34 |
7-day |
|
5/30 |
8 |
42 |
7-day |
|
5/31 |
1 |
43 |
7-day |
|
6/1 |
1 |
44 |
7-day |
|
6/4 |
17 |
61 |
5-day |
|
6/7 |
2 |
63 |
5-day |
|
6/8 |
1 |
64 |
5-day |
The
period beginning late June 4 and continuing through the 5th, 6th
and the 7th produced 61 continuous hours of humidity above our
threshold. This produced the big jump in DSV’s. Hopefully, you will be able to
apply a fungicide for disease control as soon as possible.
The
seven day spray schedule is probably the most practical for growers although
the model is calling for a 5-day spray interval at this time.
Growers
who do not want to rely only on the DSV calculations for scheduling fungicide
applications should apply mancozeb (Dithane, Pencozeb, Manex II) or Bravo
before plants canopy down the row and repeat on a 7-day schedule. Late blight
has not been a problem here in
Early Blight and Black Dot.
Many fields are flowering or approaching flowering and this is a good time to
consider switching to an application or two of Gem, Headline or Quadris
(Amistar) for early blight susceptible varieties. This can also be helpful for
late season varieties including russets if stress makes plants susceptible to
black dot. Make one or two applications at the end of flowering and repeat 14
days later.
If
pink rot control is important and
you did not treat at planting, foliar applications of either Ridomil Gold MZ or
Ridomil Gold/Bravo, or Flouronil when tubers are nickel-sized is
suggested. A second application should
be made 14 days later. For specific fungicide recommendations, see
pages F132-33, 2004

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Hollow Heart of
Watermelons – Ed Kee, Extension
Vegetable Crops Specialist; kee@udel.edu
Watermelons
have grown a lot in the past 10 days, growers are now beginning fungicide
sprays,
scouting for insects and mites, and applying nitrogen. While there is no special reason to
anticipate any excess hollow heart problem, it is a good time to discuss what
can cause this physiological problem.
Chris Wein, of Cornell writes,
“This disorder is characterized by the separation of the inner parts of
the fruit into distinct segments, leaving hollow areas at harvest
maturity. Hollow heart occurs more often
in the first-formed fruit on the plant, as a result of excess nitrogen
fertilization and delayed harvests. The
disorder is more prevalent under conditions of rapid fruit growth rate, when
the rind is expanding more rapidly than the inner regions of the fruit. Ways of avoiding the condition include
selection of less susceptible cultivars, and using cultural practices that
moderate fruit growth rate and final fruit size. These include adequate plant populations,
moderate levels of nitrogen, and prompt harvests.”
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Sandea Can Carryover to Some
Vegetables - Mark
VanGessel, Extension Weed Specialist; mjv@udel.edu
Sandea is labeled for use in a number of vegetable
and melon crops. However, it is not safe
for all vegetables and this includes vegetables planted in rotation with crops
treated with Sandea (halosulfuron). Last
year a few fields were planted with pickles, treated with Sandea, and rotated
to spinach. The spinach crop was injured
due to halosulfuron carryover. So check
your herbicide labels to be sure there are no problems with herbicide
carryover.
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Field Crop Insects -
Alfalfa.
Continue to sample all fields on a weekly basis for leafhopper adults
and nymphs. Once fields are yellow, stand and yield loss has already occurred.
We are starting to see a significant increase in nymphs which often cause
damage very quickly. The treatment thresholds are 20 per 100 sweeps on alfalfa
3 inches or less in height, 50 per 100 sweeps in 4-6 inch tall alfalfa and 100
per 100 sweeps in 7-11 inch tall alfalfa. Baythroid, dimethoate, Mustang or Warrior will provide effective
control. Early cutting is also a control option, but be sure to check fields
within a week of cutting for leafhoppers.
Field Corn
Continue to scout corn for grasshoppers feeding on small plants. A
grasshopper treatment should be considered if you find 5-8 grasshoppers per
square yard. Asana, Dimethoate, Lorsban, Furadan and Warrior will provide
control but multiple applications may be needed.
Continue to scout whorl stage corn for European
corn borer. Corn borer control will not be needed until 50% of the planted are
infested in irrigated fields and 80% of the plants are infested in dry land
fields. Since corn is growing quickly, the best time for control will be just
at pre-tassel or tassel emergence as long as larvae have not bored into the
midribs of leaves.
Soybeans.
Grasshopper and bean leaf beetle feeding continue to be found in seedling
stage soybean fields. A treatment for bean leaf beetle will be needed from
plant emergence to the second trifoliate when you find 2 beetles per ft. of row
and a 25% stand reduction. A pyrethroid, dimethoate or Lorsban will
provide control. The treatment threshold for grasshoppers is 1 per sweep and
30% defoliation. Asana, Furadan, Lorsban,
or Warrior will provide grasshopper control.
We are starting to see a significant increase in the number of thrips in
soybean. However, no treatment is needed until you find 8 thrips per leaflet,
and plant growth is being held back.
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Field Crop Diseases
-
Small Grain.
Barley
harvest is underway and from a disease perspective small grain diseases have been relatively minor compared to last
year. A few scattered fields in the northern part of the state have had some
head blight or scab (estimate at less than 1 percent) and some tan spot. At this
point rust is showing up now on any wheat that is late, but will not affect
yield. The major problem downstate appeared to be drought damage especially on
sandy knolls. Some fields have sooty mold where the drought damaged plants died
prematurely and these black fungi grow saphrophytically on the heads.
Field Corn.
Anthracnose leaf blight is showing up in scattered
areas on corn following corn and corn fodder is present. There are large
differences in susceptibility among hybrids as you can imagine. Usually
seedling infections or infection of young plants is not important and the corn
often grows out of it. If the hybrid is susceptible and favorable weather for
infection occurs later in the season, the spores from the early infection can
infect the leaves and/or stalks and cause problems later. Anthracnose stalk rot
is very common throughout
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Car