Volume 12, Issue 10
May 28, 2004
Volume 12, Issue 10
May 28, 2004
Vegetables
Pea Harvest
Progress – Ed
Kee, Extension Vegetable Crops Specialist; kee@udel.edu
Pea Harvest began 10-14 days ago and yields in most
cases have been good, ranging in the 3-4,500 pound per acre range. A few fields experienced heavy, packing rains
soon after planting and the resulting compaction and uneven stand took their
toll on yields.
In some cases, warm weather coupled with dry soil
conditions accelerated maturity, causing some acreage to be by-passed. However, this year’s pea yields and harvest
progress are very good.
Pickling Cucumber
Plantings – Ed
Kee, Extension Vegetable Crops Specialist; kee@udel.edu
Pickle planting is in full-swing, with many growers
having 6-7 plantings in the ground.
Emergence and weed control looks good to date. We will be planting our variety trials in
June at Fifer Orchards near Camden-Wyoming, and in July at Richard Carlisle’s
Pine Breeze Farms, in
In the May 7 issue of Weekly Crop Update, the use
of Sandea as a post-emergence weed control material was discussed. Briefly, it is labeled at 0.5-0.66 ounces per
acre and will control red-root pigweed, nutsedge, along with other problem
weeds.
Lima Bean
Fertilizer Programs – Ed
Kee, Extension Vegetable Crops Specialist; kee@udel.edu
Lima bean planting has just begun. Our recommendation for single-crop lima beans
calls for 60-80 pounds of Nitrogen per acre.
This can be applied broadcast, or split into applications broadcast,
at-planting, and sidedressed; or some combination of the three. Research data and commercial experience has
not consistently demonstrated a clear advantage of one timing or another.
The recommendation for nitrogen for lima beans
planted after peas is 0-20 pounds of nitrogen per acre. Of course, there is significant residual
nitrogen from the peas that allows this reduction.
Phosphorus and Potassium should be applied
according to soil test recommendations.
However, if the soil is testing high or excessive, no phosphorus is
required, especially after peas, and potassium at 50-75 pounds per acre is appropriate.
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.
Actara, Fulfill, Thiodan
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. 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. Actara, Fulfill, Lannate and Thiodan are labeled on
melons and will provide melon aphid control.
Continue to watch
fields carefully for cucumber beetles. Be sure to look under the plastic where
beetles can often hide until disturbed. We have found a number of fields with
high levels and beetles can be found in most fields.
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 there is no corn in the 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.
Although there are no available thresholds, a treatment may be needed if you
see populations increasing. Baythroid, Capture, Spintor and Warrior will provide thrips
control.
Potatoes.
Colorado potato beetle
(CPB) adults, egg masses and the small to medium size larvae can be
found in fields where an at-planting CPB material was not used. A
treatment should not be needed for adults until you find 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.
Avaunt + PBO, Actara, cryolite,
Spintor or Provado will
provide control. Corn borer catches have increased in some areas and 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. We are also finding economic
levels of potato leafhopper adults in the earliest planted 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.
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. 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. In addition, we have started
to find the first corn earworm moths. The first silk sprays will be needed as
soon as ear shanks are visible. Treatment will be needed on a 5-day schedule in
Vegetable Diseases –
Fusarium wilt in watermelon has been detected in
several fields on Delmarva this spring.
Symptoms in new transplants are stunted growth, necrotic leaves,
wilting, and a distinct vascular discoloration.
Infected fields may appear to recover; however symptoms often reappear
later in the season when the vines produce runners. Wilting then becomes more severe as fruit
increase in size and plants appear water-stressed even under conditions when
soil moisture is adequate. Wilt occurs
on crown leaves first, then on runners and eventually on the whole plant. Infected stems may have a red, brown or black
gummy exudate and the vascular system of the plant is discolored.
Management of Fusarium wilt has been accomplished
in the past through long rotation (5 to 6 years), planting resistant cultivars,
and fumigation. However, fumigation may
fail to control the disease because Fusarium can quickly reinvade fumigated
ground. A new aggressive form of the
pathogen (Fusarium oxysporum f. sp niveum, race 2) has been
detected in
|
|
|
Wilt (%) |
Marketable fruit yield |
|
|
Cultivar |
Source |
No./A |
t /A |
|
|
Millionaire |
Seedway........................................ |
97 a * |
293 ab |
1.6 ab |
|
Triple Star |
Seedway........................................ |
93 a |
440 ab |
2.0 ab |
|
Genesis |
Seedway........................................ |
93 a |
0 a |
0.0 a |
|
Seedway 4502 |
Seedway........................................ |
87 a |
733 ab |
4.3 ab |
|
Sugarheart |
Siegers........................................... |
80 a |
880 b |
4.7 b |
|
Millennium |
Seedway........................................ |
53 b |
293 ab |
1.5 ab |
|
Seedless Sangria |
Siegers........................................... |
7 c |
1467 c |
9.7 c |
*Mean values in each column followed by the same letter
are not significantly different at P
= 0.05 according to Fisher’s protected least significant difference test.
The weather-based forecasting program MELCAST has
begun for 2004. MELCAST was developed at
To use MELCAST for watermelons, apply the first
fungicide spray when the watermelon vines meet within the row. Additional sprays should be applied using
MELCAST. Accumulate EFI (environmental
favorability index) values beginning the day after your first fungicide
spray. Apply a fungicide spray when 30 EFI values have accumulated at the
weather location nearest your field. Add
2 points for each overhead irrigation that is applied to the field. After a fungicide spray, reset your counter
to 0 and start over. If a spray has not
been applied in 14 days, apply a fungicide, reset the counter to 0 and start
over.
In addition to MELCAST for Watermelon, we have two
models that are designed to help you make decisions on when to spray for
diseases. MELCAST for Cantaloupes is a
fungicide application program for Alternaria leaf blight. It can be used by anyone growing a powdery
mildew resistant variety such as Athena.
To use MELCAST for Cantaloupe, apply the first fungicide spray when the
cantaloupe vines meet within the row.
Additional sprays should be applied using MELCAST. Accumulate EFI (environmental favorability
index) values beginning the day after your first fungicide spray. Add 2 points for each overhead irrigation
that is applied to the field. Apply a
fungicide spray when 20 EFI values
have accumulated at the weather location nearest your field. After a fungicide spray, reset your counter
to 0 and start over. If a spray has not
been applied in 14 days, apply a fungicide and reset the counter to 0 and start
over.
TOMCAST is a spray forecaster for leaf blights and
fruit diseases of processing tomato.
However, it does not work for bacterial diseases. In fields that are not
rotated away from tomatoes and in late-planted fields, begin sprays shortly
after transplanting. In all other areas
begin sprays when crown fruit are one-third their final size. Additional sprays can be scheduled using
TOMCAST. Sprays should be applied after
accumulating 18 DSV’s (disease severity values) since the last fungicide
application. Scout fields for late
blight. If late blight occurs additional
sprays are warranted (see Delaware Extension Bulletin 137). Note:
We provide TOMCAST data at the request of interested growers.
However, we have not tested the model in our area and don’t have the resources
to adequately support it. Please use it
on small acreage to become comfortable with it.
The three disease models are available at http://www.agnr.umd.edu/users/vegdisease/vegdisease.htm. In addition you can receive the models by
e-mail or fax. To sign up, please call
Vegetable Crops Diseases -
Potatoes.
Late Blight Advisory.
We
are using the E-WEATHER SERVICE from SkyBit, Inc. as we have in the past. The service determines specific requested weather
parameters (temperature, relative humidity and rainfall) at Joe Jackewicz’s
farm based on calculations of data from the nearest National Weather Service
stations. This weather data is used in
the WISDOM software program for predicting late blight and making spray
recommendations.
Disease
Severity Value (DSV) Accumulation as of
|
Date |
Daily DSV |
Total DSV |
Spray Recommendation |
|
4/25-
5/2 |
4 |
4 |
none |
|
5/3 |
8 |
12 |
none |