Volume 12, Issue 11
June 4, 2004
Vegetables
Vegetable Crop Insects -
Cucumbers.
All fields should be scouted 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. We continue to see an increase in the number of fields with spider mite
infestations. If populations are high at the time of treatment, 2 sprays spaced
5 days apart may be needed. The threshold for mites is 20-30% 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% 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.
Fields should be sampled for thrips
and corn borers. Although corn is
growing rapidly and should be more attractive to corn borer moths, you should
still watch for corn borer egg masses in isolated fields ( i.e. not near corn
fields). You should also check local moth catches in your area (http://www.udel.edu/IPM/traps/latestblt.html
). A treatment with a pyrethroid
may be needed if corn borer moth catches exceed 10 moths per night, especially
if corn planting is delayed in your area or you are using rye strips as
windbreaks. In general, 2 applications will be needed to achieve
effective control. Thrips
can cause damage in peppers by vectoring tomato spotted wilt virus and by
causing direct plant damage. There have been reports of tomato spotted wilt in
tomatoes in
Potatoes.
Colorado potato beetle (CPB) adults and larvae
can be found in many fields, even where at planting treatments were used. The
treatment threshold for adults is 25 beetles per 50 plants and defoliation has
reached the 10% level. Once larvae are detected, the threshold is 4 small
larvae per plant or 1.5 large larvae per plant. The threshold for each should
be reduced if all stages of larvae are present. Avaunt + PBO, Actara, cryolite, Spintor or Provado will provide
control. Corn borer sprays will now be needed 3-5 days after an increase in
trap catches. Be sure to check our website http://www.udel.edu/IPM/traps/latestblt.html)
for the most recent moth catches in your area. Avaunt, Ambush, Baythroid, Furadan, Penncap, Pounce or Spintor will
provide control. If you are scouting for infested terminals, the first
treatment should be applied when 20-25% of the terminals are infested. Furadan or Monitor will provide the best control if you are
waiting until you see infested terminals. 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 ˝ 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. As soon as the earliest fields have buds present, a
treatment will be needed for corn borer control once moth catches are above 2 per night in your
area. 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.
Flea beetles and cutworms are still active in
seedling stage sweet corn. The treatment threshold for flea beetles is 5%
infested plants. The cutworm threshold is 3% cut plants or 10% leaf feeding. We are also seeing cereal
leaf beetle adults in seedling and whorl stage corn. A treatment may be needed
if you find 10 beetles per plant and 50% of the plants exhibit damage.
Continue to sample any corn in the whorl stage to pretassel stage for European
corn borer larvae. A treatment should be applied if 15% of the plants are
infested. In recent years, Avaunt (whorl stage only), Baythroid,
Mustang, Penncap, Spintor or Warrior has provided effective control. If economic levels of corn
borers are present in pretassel to tassel stage corn, two sprays spaced 3-4
days apart are often needed. The first silk sprays will be needed for corn
earworm as soon as ear shanks are visible. Treatment will be needed on a 5-day
schedule.
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Bee Kills in Watermelons –

Bee
kills in watermelons is a serious problem. Everyone loses when it happens. The
bee keeper loses his bees and the grower loses the pollination service. Unfortunately, materials act
differently. Some kill the worker bees
in the field during spraying. Others can
be carried by the field workers from the field to the hive. Larvae are then killed. If the brood larvae are affected, you are
looking at a 21 day set back before the queen will lay new eggs and new workers
are available to care for the hive. It is economically important for growers to
protect the bees that are in your field.
We recently looked at a field where most of field
force was killed off. We think the hives will recover, but it will take time to
replace the field force and build up the colony strength. As a grower, you can help reduce the problem
of bee kills by informing the bee keeper of when you are going to apply bee
killing materials. Spray late in day when there are fewer bees in the
field. Alert the applicator to hive
location to avoid direct spraying of hives.
Select the safest material that works. You can provide additional
protection for the bee hives by sitting your overhead irrigation system over
the hive and run the system while the field is being sprayed. Another trick is
to soak burlap with water and cover the hives to keep them in and cool. This would probably be the only way to
protect hives sitting in the field. You have to remove the burlap right after
spraying to prevent them from getting too hot and being killed by the heat. In
the past, we used to just use local bee keepers. They could come protect their
hives. Commercial bee keepers cannot
make it around to all of the sites to protect their bees. A lack of bees will
cost growers quality and yield. Can you afford not to help protect them?
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Vegetable Crop Diseases
-
Late
Blight Advisory
Disease
Severity Value (DSV) Accumulation as of June 2, 2004, is as follows:
|
Date |
Daily DSV |
Total DSV |
Spray Recommendation |
|
4/25-
5/2 |
4 |
4 |
none |
|
5/3 |
8 |
12 |
none |
|
5/9 |
2 |
14 |
none |
|
5/13 |
1 |
15 |
none |
|
5/17 |
2 |
17 |
none |
|
5/18 |
1 |
18 |
none |
|
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 |
All potatoes in DE have accumulated 18 DSV’s or
more by now. The threshold of 300 P-days was also exceeded yesterday, which
would recommend initiating sprays for early blight. This will be important for
growers with early blight susceptible varieties. This 300 P-day threshold was
exceeded for potatoes that emerged on or before April 25.
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
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Management Strategies for Phytophthora Fruit
Rot Control in Pickling Cucumbers -
and Ed Kee, Extension Vegetable Specialist,
Phytophthora
fruit rot can be a devastating disease of pickles on Delmarva. Last year’s wet
season was a very favorable year for Phytophthora
capsici on many crops. The fungus is soilborne and the overwintering oospores
can remain viable in the soil for 10 years or more. Cultural practices that
help control Phytophthora are (1) as long a rotation away from susceptible
crops (tomatoes, peppers, eggplants, lima beans, cucurbits including pumpkins,
summer and winter squash, watermelon, and cantaloupe) as possible, (2) plant
only well-drained fields, (3) use as
wide a row spacing as possible to allow drying and reduce humidity. Properly constructed raised beds can also
be helpful as they keep vulnerable plants from saturated soil conditions. The
most effective control measure that growers have available is to avoid planting
in infested soil and limit the spread of the disease to clean fields.
Fungicides have also been shown to provide some control if applied at the right
time and good coverage is achieved. A combined approach of all available
control methods is more effective than using just one control measure.
Recent work done in Michigan by Dr. Mary
Hausbeck and her team over the past several seasons to control Phytophthora
fruit rot has promise for us here in Delaware. We have relied on applications
of Ridomil Gold or Ultra-Flourish in a band at planting followed by several
applications of Acrobat or Gavel combined with a copper fungicide such as Champ
or Kocide for
fruit rot control. Their research is
showing the best control under their conditions with three applications of
Acrobat or Gavel when fruit are
1, 3, and 5 inches long. Under our
conditions, fruit may size so quickly that only two sprays at
1 and 3 inch long fruit would be used here.
Application of the fungicides is also very important. All the fungicides for
fruit rot control which includes Acrobat, Gavel (zoxamide plus mancozeb),
mancozeb (Dithane DF, Manzate, Penncozeb) and copper hydroxide (Champ, Kocide)
are not systemic, so coverage of the fruit is very important if control is to
be effective. It is not enough to just spray until the leaves are wet, you need
enough pressure and/or air to drive the fungicide to the fruit. They have had
good success with conventional spray rigs equipped with 8003 nozzles, spaced 20
in. apart operating at 60 psi, delivering 30 gal/A. Air-assisted sprayers with
4 nozzles spaced 60 in. apart, delivering 10 gal/A have also been demonstrated
to be very effective.
Fungicide test plots and large
demonstration plots have shown that several treatments have proven effective
under varying amounts of disease pressure. As mentioned before, Acrobat 50 WP
(6.4 oz/A) or Gavel 75DF (2 lb/A) are applied with 2 lbs. of Kocide or Champ when
they are applied. They are getting slightly better control compared to the
untreated check by alternating Gavel with Acrobat. Since Gavel contains
mancozeb it has a 5 day pre-harvest interval (phi) which limits its use close
to harvest. They were applying Gavel at the 1 and 3 in. stage and ending with
Acrobat at the 5 in. size. There was no significant difference between all
three sprays of either Acrobat or Gavel.
All that being said, we would recommend for Delaware growers that they choose their fields wisely following the non-chemical guidelines add