Volume 12, Issue 22
August 20, 2004
Vegetables
Update on
Post-Emergence Weed Control in Spinach – Ed
Kee, Extension Vegetable Crops Specialist; kee@udel.edu
Stinger
is labeled as a post-emergence herbicide for use on spinach. It can be
applied when the spinach is in the
![]()
Downy Mildew on
Cucurbits – Ed Kee, Extension
Vegetable Crops Specialist; kee@udel.edu
Over
the past few weeks, we have written much about the control of Downy mildew on
cucurbits. It has been devastating, with
serious yield loss on watermelons, significant damage to pumpkin vines, and
very serious yield loss and quality damage to pickling cucumbers. In the case of pickles, even with good yields
at the beginning of the season, final production may only approach 50% of
intended production.
With
the innoculum coming to us early in the season and in apparently unprecedented
amounts, this threat was compounded by cool, wet weather that favored the
development of the disease. In the 46 days between July 1 and August 15,
it rained 28 days; or 60% of the days experienced rain. There were two
stretches of six consecutive days of rain during this time frame. There
were no days in this period with temperatures above 90oF at the
University of Delaware Research & Education Center’s weather station near
As
reported earlier, a period of at least six hours of 100% relative humidity at
the leaf surface is required for the disease organism to produce
sporangia. We certainly had extended periods of these conditions, which
helped launch and maintain the epidemic of Downy mildew.
Some
observers have inquired about the appearance of the plants and possible
fertility deficiencies. The pale, weakened appearance is a result of the
Downy mildew, not plant nutrition problems. The rates applied this year
are consistent with previous years, when vine growth was aggressive, in fact,
perhaps too aggressive. We have one field with over 175 pounds/A of
nitrogen applied in an attempt to stimulate the plant, and are not seeing any
significant response.
Many
fields still exhibit the symptoms and damage continues. However, we are
seeing some plantings that were sprayed frequently and often, holding their
own. While we work towards solutions for this year’s crop, we are turning
our attention to avoiding and preventing a similar situation next year.
Although in the unlikely event the weather pattern repeats itself, the
battle will be engaged again.
![]()
Vegetable Crop Insects -
Cabbage.
Continue to sample
fields for diamondback
and cabbage looper larvae. Economic levels can now be found. A treatment should be considered if you find
5% of the plants infested and before they move into the hearts of the plants.
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. Since earworm continues to be
found in lima bean fields, be sure to scout fields with pin pods for corn
earworm. A treatment will be needed if you find one corn earworm larvae per 6
ft of row. Capture, Lannate, Mustang or Warrior will provide earworm control.
The higher rates may be needed if population levels are high and worms are
large at the time of treatment.
Peppers.
Be sure to
maintain a 5-7 day spray schedule for corn borer, corn earworm, beet armyworm
and fall armyworm control.
Snap Beans.
At this time, all fresh market and processing snap
beans will need to be sprayed for corn borer and corn earworm control from the
bud stage through harvest. Remember, Orthene provides poor corn earworm
control. Since trap catches change quickly and we are seeing another spike in
corn earworm moth catches, 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).
Spinach.
Since webworm and beet armyworm moths are both actively laying eggs, be
sure to watch for both worm pests as soon as plants emerge. Controls should be applied when worms are small and
before they have moved deep into the hearts of the plants. Also, remember that
both insects can produce webbing on the plants. Since beet armyworms are more
difficult to control, chemical selection is important. Confirm, Intrepid or
Spintor will be needed for beet armyworm control. If webworms are the
predominant species, permethrin, Confirm (8 oz/acre),or Intrepid (8-10 oz)
should be used. Generally, at least 2 applications are needed to achieve
control of webworms and beet armyworm.
Sweet
Corn.
With the
recent increase in corn earworm trap catches, all
fresh market silking sweet corn should be sprayed on a 2-day schedule. 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).
![]()
Vegetable Crop Diseases - Bob Mulrooney, Extension Plant
Pathologist, bobmul@udel.edu
Lima beans.
Downy Mildew Alert. Downy mildew, caused by Phytophthora phaseoli, was positively
identified in two samples from the
Downy mildew on
![]()
LATE BLIGHT ADVISORY. NOTE: This will be the last potato
disease advisory.
Disease Severity Value (DSV) Accumulation as
of
|
Date |
Daily DSV |
Total DSV |
Spray Recommendation |
|
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 |
|
8/4 |
2 |
163 |
5-day |
|
8/6-8/11 |
0 |
163 |
10-day |
|
8/11 |
1 |
164 |
7-day |
|
8/12 |
4 |
168 |
5-day |
|
8/13 |
2 |
170 |
5-day |
|
8/14 |
4 |
174 |
5-day |
|
8/15 |
3 |
177 |
5-day |
|
8/16 |
2 |
179 |
5-day |
|
8/17 |
2 |
181 |
5-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-NJ area on potatoes.
Note: Late blight has been confirmed on tomato in
![]()
Field Crop Insects -