Volume 12, Issue 20
August 6, 2004
Vegetables
Vegetable Crop Insects -
Cabbage.
Be
sure to sample fall planted fields for diamondback and cabbage looper larvae.
We can find both insects in recently planted fields. If both species are
present, Avaunt, a Bt, Proclaim or
Spintor will provide control. If
cabbage looper is the predominant species, a pyrethroid, Intrepid, or
Confirm will also provide control.
Lima Beans.
Continue to scout for lygus bugs and
stinkbugs as soon as pin pods are present. Treatment should be considered if
you find 15 adults and/or nymphs per 50 sweeps. You should also start scouting
fields with pin pods for corn earworm. A treatment will be needed if you find
one corn earworm larvae per 6 ft of row from late flat pod stage until harvest.
Capture, Mustang, Lannate or Warrior
will provide corn earworm control.
Melons.
Continue to scout all melons for aphids, cucumber beetles, and spider
mites. Be sure to watch for bees foraging in the area and avoid insecticide
applications on blooming crops.
Peppers.
Be sure to maintain a 5-7 day spray schedule for corn borer control.
Since corn earworm populations are starting to increase in many locations, you
will also need to consider treating for corn earworm. Continue to
scout for beet armyworm, especially if fields are weedy. Avaunt, Intrepid and Spintor will provide the
best beet armyworm control.
Snap Beans.
At this time, all fresh market and processing snap beans will need
to be sprayed for corn borer from the bud stage through harvest. With the increase
in corn earworm trap catches, you will also need to consider this pest when
making your chemical selection. Remember, Orthene provides poor corn earworm
control. So if Orthene is used at the pin stage, a pyrethroid should be added
to the mix. Since moth catches can change quickly, be sure to check our website
for the most recent trap catches and information on how to use this information
to make a treatment decision in processing snap beans. (http://www.udel.edu/IPM/traps/latestblt.html
and http://www.udel.edu/IPM/thresh/snapbeanecbthresh.html).
Sweet Corn.
All fresh market silking sweet corn should be sprayed on a 2-3 day
schedule. Since corn earworm populations
have increased quickly in some locations, be sure to check trap catches
frequently. You can check trap catches and treatment decision guidelines on our
website (http://www.udel.edu/IPM/traps/latestblt.html
and http://www.udel.edu/IPM/thresh/silkspraythresh.html).
Continue to watch for fall armyworm feeding in the whorls. A treatment is
needed if you find 12-15% of the plants infested. Generally, 2-3 whorl sprays
are needed to achieve control. In whorl stage corn, Avaunt, Lannate, Larvin and
the high rate of Warrior have provided the best control in recent years. In
addition, we also have a 24C SLN label for Lorsban 4E for armyworm control in sweet
corn. With all products, the best control will be achieved if worms are small
at treatment time. Also be sure to check
all labels for grazing restrictions and feeding restrictions for corn silage,
forage or fodder. In addition, if fall
armyworm pressure is heavy in your whorl stage fields (above 30% infested
plants), you should consider a combination of a pyrethroid plus Lannate, Larvin
or Lorsban for the first 1-2 silk sprays.
Be sure to check labels for days between last application and harvest for
all materials.
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Lima Bean Fields
Are Being Sprayed for Downy Mildew Prevention –
Ed Kee, Extension Vegetable Crops Specialist; kee@udel.edu
With
conditions favorable for the development of Downy mildew (Phytophthora phaseoli) on
lima beans, many processors, consultants, and growers are taking steps to
prevent Downy mildew on lima beans.
While no outbreaks have been reported in commercial fields, we have seen
some Downy mildew on home garden pole lima beans. Typically, preventative applications of a
fixed copper (Champ DP or Kocide 2000) are being applied, often in conjunction
with insect sprays, but not necessarily.
If
Downy mildew is suspected or found on lima beans, please contact your county
agent, an Extension plant pathologist, or me.
We are interested in determining what races of Downy are present.
This
Downy mildew is a different species of fungus from the Downy mildew fungus that
attacks cucurbits (Pseudopersonospora
cubensis).
Please
refer to Issue 19 for specific spray recommendations.
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Downy Mildew on
Pickling Cucumbers – Ed
Kee, Extension Vegetable Crops Specialist; kee@udel.edu
This
Downy mildew (Pseudopersonospora cubensis)
is still plaguing all cucurbit crops, including watermelons, cantaloupes,
pumpkins, squash, and cucumbers. Yields
of pickling cucumbers are reduced from the inability of the plant’s foliage to
support fruit growth and from the interruption of pollination due to the
adverse impact on the pollinator varieties.
The latter situation is especially true with varieties that use older,
less resistant pollinators, and results in a high percentage of unusable fruit.
Early
reports from
If
there is any good news in all of this, it is that this organism does not over
winter in our region. The source of
primary innoculum for our region is considered to be wind-borne sporangia from
infected cucurbits grown in areas to the south of us. Historically, the conventional wisdom has
identified
As
a reminder, this fungus infects only members of the Cucurbitacae family.
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Spinach Planting
Will Begin Soon – Ed
Kee, Extension Vegetable Crops Specialist; kee@udel.edu
Spinach
plantings for fall harvest will begin soon.
Successful weed control programs in the past have utilized Ro-Neet used
as a pre-plant incorporated material, and Dual as a pre-emergence material. Ro-Neet can be applied at 3-4 pints/acre and
incorporated into the soil at 2-4 inches.
This should be done 7 to 10 days in advance of planting to reduce
potential injury. Ro-Neet will do a good
job of controlling most grasses and the broadleaf weeds pigweed and purslane. It will do a fair job on common lambsquarter.
Dual
Magnum has a 24c special local needs label for pre-emergence control of weeds
in spinach. This label is in place for
If
Ro-Neet and Dual are going to be used, consideration should be given to
reducing the Ro-Neet rate to the 2-3 pint range, again to help avoid potential
injury.
Post-emergence
herbicides such as Poast 1.5 EC and Select 2EC are available for grass control
later in the season if necessary. Spin-aid is available for post-emergence
control of chickweed and other broadleaf weeds in the fall months only.
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Vegetable Crop Diseases - Bob Mulrooney, Extension Plant
Pathologist, bobmul@udel.edu
Late Blight Advisory.
Disease Severity
Value (DSV) Accumulation as of August 4, 2004 is as follows:
|
Date |
Daily DSV |
Total DSV |
Spray Recommendation |
|
6/26-30 |
0 |
87 |
10-day |
|
7/1-7/11 |
7 |
94 |
10-day |
|
7/12 |
5 |
99 |
7-day |
|
7/13 |
2 |
101 |
7-day |
|
7/14 |
2 |
103 |
7-day |
|
7/17 |
10 |
113 |
5-day |
|
7/19 |
1 |
114 |
5-day |
|
7/22 |
2 |
116 |
7-day |
|
7/23 |
2 |
118 |
7-day |
|
7/24 |
9 |
127 |
7-day |
|
7/26 |
5 |
132 |
7-day |
|
7/27 |
11 |
143 |
5-day |
|
7/29 |
2 |
145 |
7-day |
|
7/30 |
10 |
155 |
7-day |
|
8/2 |
4 |
159 |
7-day |
|
8/3 |
2 |
161 |
7-day |
Application
rates for protectant fungicides (Dithane, Bravo, etc.) should be at the high
end of the rate with the amount of foliage present. For specific fungicide
recommendations, see pages F132-33, 2004 Delaware Commercial Vegetable
Production Recommendations Book. EB 137.
No
late blight has been seen in DE-MD area on potatoes.
Note: Late blight has been confirmed on tomato in

Photo by Bob Mulrooney
Late blight on tomato leaf.
Note
the white ring of the late blight fungus sporulating on the edge of the lesion.
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Field Crop Insects -
Soybeans.
We continue to find low levels of
soybeans aphids in all three counties.
You will need to look at the entire plant when sampling for aphids. The
treatment threshold is 250 per plant up to growth stage R-3/R-4 with 80% of the
plants at that level. After R4, the
threshold increases to 1,000-1,500 aphids per plant. Numerous products are
now labeled for soybean aphid including Asana, Baythroid (suppression only),
Mustang MAX, Warrior, and Lorsban. Dimethoate has not provided adequate control
and Furadan 4F only has a 2ee label for the Midwestern states.
We are starting to find a few
corn earworms in double cropped fields; however, populations are extremely low
at this time. With the increase in moth catches in
The following materials will
provide corn earworm control in soybeans: Ambush, Baythroid, Asana, Mustang
MAX, Pounce, Warrior (all pyrethroids), Larvin, Lorsban or Steward. Larvin and Steward act by ingestion on both
small and large larvae. Remember that if you are using a pyrethroid, the
primary mode of action on large larvae will be ingestion. Earworms will need to feed to cause death so you will not see much
activity from the contact action. Once they ingest the product, they
immediately stop feeding. Therefore, fields should not be evaluated for control
until 4 days after application. Small
larvae are generally killed by contact as well as ingestion. It is important that you do not look at
fields 1-2 days after spraying and assume control failure if large worms are
present. This could result in unnecessary re-sprays. We are also finding a few
beet armyworms in fields. If the predominant pest is beet armyworm, the
pyrethroids will not provide control. Steward would be the preferred material. However,
in 2002 grower demonstration trials, Lorsban also provided good control.
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Field Crop Diseases - Bob Mulrooney,
Extension
Plant Pathologist, bobmul@udel.edu
Corn.
Leaf blights and spots are on the increase. Northern corn leaf spot often called Carbonum leafspot rac