Volume 12, Issue 14
June 25, 2004
Volume 12, Issue 14
June 25, 2004
Vegetables
Vegetable Crop Insects -
Cucumbers.
We continue to see an increase in aphid
populations. 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.
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
and aphid infestations. 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% 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. We just received our 24C label allowing
aerial application of Acramite on melons. Only one application is permitted per
season and the rate is 1 lb/acre. This registration remains valid, unless
disapproved by EPA within 90 days of issuance, for 5 years (Federal) and one
year (
Peppers.
In
areas where corn borer trap catches are above 2 per
night and pepper fruit is ˝ inch in size or larger, fields should be sprayed on
a 7-10 day schedule for corn borer control.
You will also need to consider a treatment for pepper maggot. If Orthene
is used, it will also provide pepper maggot control. Otherwise, dimethoate
should be added to the mix.
Potatoes.
Continue
to scout fields on a weekly basis for Colorado potato beetle
(CPB)
adults and larvae. 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 ˝ if
all stages of larvae are present. Avaunt + PBO, Actara, cryolite, Spintor, Provado or newly labeled Rimon will provide control. We
just received our state label for Rimon. Although labeled at 9-12 oz/acre, the
12 oz rate is recommended. Remember from the last newsletter, it will
not control adults and has buffer zone and buffer strip restrictions for aerial
application. We are also starting to see the emergence of summer
adults. Unfortunately, most of our labeled products are most effective on
larvae. The higher labeled rates of Spintor and cryolite have provided some
level of adult suppression; however, may not be adequate under high population
pressure. Actara, Leverage and Provado provide adult control but should not be
used where Admire, Platinum or Gaucho were used at planting to avoid
development of resistance. Economic
levels of potato leafhopper adults and nymphs can still 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. We have just found our first green peach aphids in potatoes. No
controls will be needed until you find 2
aphids per leaf during bloom and 4 aphids per leaf post bloom. If melon aphids
are found, the threshold should be reduced by ˝. If green peach aphid is the predominant
species, Fulfill, Lannate, Monitor, Provado, or Vydate will provide control. If
Fulfill is used, a penetrating surfactant should be used to achieve good
coverage and achieve optimum control.
Snap Beans.
All
seedling stage beans should be scouted for leafhopper and thrips activity. 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. Since this 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
silking sweet corn should be sprayed on a 5- 6 day schedule. 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 silking sweet corn (http://www.udel.edu/IPM/traps/latestblt.html
and http://www.udel.edu/IPM/thresh/silkspraythresh.html).
Pickling Cucumber
Harvest Begins – Harvest Timing Means $$$ – Ed
Kee, Extension Vegetable Crops Specialist; kee@udel.edu
Pickling
Cucumber Harvest began last Saturday, one of the earliest starts in memory. This reflects the warm growing conditions we
experienced through most of the spring, and probably more sunshine than usual.
Growers
are reminded that choosing the proper day for harvest can make a significant
positive economic impact. With the once-over
destructive harvest and the contract structured for different values for
different size pickles, the gross return on any given harvest is directly
affected by maturity. A good “rule of
thumb” is to harvest when 5% (by weight) of the pickles reach the 4A category,
or between 2 and 2/18 inches. Probably
70 to 80% of the load is in the 3A (1.5 to 1.75 inches) and 3B (1.75 to 2.00
inches) categories. This seems to
reflect the proper compromise between weight and declining value for the
largest sizes.
Many
growers sample 2-3 days prior to harvest to track the rate of maturity. Growers are also encouraged to “do the math”
when they get their grade sheets on particular loads. Run the calculations based on the contract
prices of each size and the percent of the load in each size. Change the percentages and do the
calculations to see how the value of the load can be affected by harvest
timing.
Emerged Lima Beans Can Be Injured With Dual -
Mark VanGessel, Extension Weed Specialist; mjv@udel.edu
Dual is labeled and quite safe for preemergence use
on lima beans. However, I have seen
fields and situations when Dual was applied as the beans were just emerging, or
lima beans followed a small grain that was only disked in. Only disking it in resulted in poor soil
coverage of the lima bean seed. In these
situations, lima bean injury can occur.
To avoid these problems, be sure the seed slit is filled in with soil
and do not delay application more than one to two days after planting.
Bee Hive Strength Related to Fruit Set – Derby
Walker, Sussex County Extension Ag Agent, derby@udel.edu;
Tracy Wootten, Extension Horticulture Agent, wootten@udel.edu
We have received questions on pollination of
watermelon fields this week. Lack of
good pollination can be a result of weak bee hives. A good hive should have 6 frames of brood with
enough bees for 8 frames. Information on evaluating honey bee colonies for
pollination can be found at the following Pacific Northwest Extension
Publication: http://wwwagcomm.ads.orst.edu/AgComWebFile/EdMat/PNW245.pdf. Information on what is a colony, worker bees,
colony size and efficiency, colony strength, disease, amount of comb, number of
bees, food requirement, a normal queen and colony flight is discussed. As mentioned in
Manganese Toxicity on Muskmelon – Derby
Walker, Sussex County Extension Ag Agent, derby@udel.edu;
Tracy Wootten, Extension Horticulture Ag, wootten@udel.edu
Manganese
toxicity on muskmelon was observed this week.
Characteristic signs in the field are yellowing, lighter green spotting
on the upper surface of the leaf and watersoaked “pin holes” on the lower
surface of the leaf. Holding the leaf up
to the light will help with diagnosis.
These areas will become necrotic, and eventually the whole leaf will
die. Manganese toxicity is the result of
low pH – below 6.0. Unfortunately, this
usually does not reveal itself until approximately 2 weeks before harvest. We experienced this at the
http://www.rec.udel.edu/veggie/manganese.htm
Vegetable Crop Diseases -
Extension
Plant Pathologist, bobmul@udel.edu
Late Blight Advisory.
Disease Severity Value
(DSV) Accumulation as of
|
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 |
|
6/10-6/13 |
9 |
73 |
7-day |
|
6/14-6/15 |
3 |
76 |
7-day |
|
6/16 |
3 |
79 |
7-day |
|
6/17 |
3 |
82 |
7-day |