Volume 11, Issue 23
August 29, 2003
Volume 11, Issue 23
August 29, 2003
Vegetables
Vegetable Insects
-
Cabbage.
Continue to sample for diamondback and cabbage looper larvae. We can find economic levels of both insects in fall cabbage fields. The treatment threshold is 5% of the plants infested. If both species are present, Avaunt (3.5 oz/acre), a Bt, Proclaim (3 oz/acre),or Spintor (4-5 oz per acre) will provide control. If cabbage looper is the predominant species, a pyrethroid, Intrepid (8 oz/a) or Confirm (8 oz/acre) will also provide control.
Cucumbers.
Consultants have started to report an increase in aphid populations in pickling cucumbers. We are also starting to see an increase in fresh market cucumbers. A treatment should be applied if 10 to 20 percent of the plants are infested with aphids. Lannate (3 days to harvest) should provide aphid control. Fulfill will also provide control. A penetrating surfactant (e.g. LI-700 or AD-100) is recommended with Fulfill (14 days to harvest). Thiodan has also provided control as long as populations are not exploded at the time of application.
Lima
Beans.
Continue to scout fields for lygus bugs, stinkbugs and corn earworm. For lygus and stink bugs, treatment should be considered if you find 15 adults and/or nymphs per 50 sweeps. A treatment is recommended for corn earworm if you find one worm per 6 foot of row.
Peppers.
At the present time, all peppers that have fruit ½ inch in size or larger should be sprayed on a 5-7 day schedule for beet armyworm, corn borer, corn earworm, and fall armyworm. Consultants are also starting to see an increase in aphid populations. If aphids are present and leaves are not curling, Lannate at 1.5 pt/A (3 days to harvest) should provide control. Actara (0 days to harvest), Assail (7 days to harvest), Fulfill(0 days to harvest), and Provado (0 days to harvest) will also provide aphid control. A penetrating surfactant should be used with Fulfill. We have also had a report of spider mites in peppers. Agri-Mek, Capture or Kelthane are labeled for spider mite control in peppers.
Snap
Beans.
Sprays are still needed at the bud and pin stages on
processing snap beans for corn borer control. A corn earworm material will also
be needed at the pin spray for corn earworm.
After the pin spray, sprays will be needed on a 5-day schedule until
harvest, except in the
Spinach.
As soon as plants emerge, fields should be scouted for webworm and beet armyworm larvae. 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. Confirm, Intrepid or Spintor will be needed for beet armyworm control. If webworms are the predominant species, Ambush, Pounce, Confirm (6-8 oz/acre), Intrepid (8-10 oz/acre) or Spintor (4-8 oz/acre) should be used. Generally, at least 2 applications are needed to achieve control of webworms and beet armyworm.
Sweet
Corn.
Fresh market silking sweet corn should be sprayed on a 2-3 day schedule throughout the state. 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 fresh market sweet corn (http://www.udel.edu/IPM/traps/latestblt.html and http://www.udel.edu/IPM/thresh/silkspraythresh.html ).
UD IPM Black Light and Pheromone Trap Counts
Average Number of Moths per Night: August 22 to
|
Trap Location |
European Corn Borer Black Light |
Corn Earworm Black Light |
Corn Earworm Pheromone Trap |
|
|
|
|
|
|
1 |
5 |
16 |
|
|
6 |
18 |
5 |
|
|
Killens Pond |
1.5 |
9 |
0.5 |
|
Little Creek |
0 |
9 |
- |
|
0.5 |
8 |
16 |
|
|
0.5 |
7 |
28 |
|
|
0.5 |
5 |
3 |
|
|
|
|
|
|
|
1 |
6 |
2 |
|
|
|
1 |
4 |
1 |
|
0.5 |
2.5 |
1 |
|
|
14 |
29 |
- |
|
|
1 |
4 |
1 |
|
|
0.5 |
5 |
3.5 |
* Numbers can change
quickly. For the most recent trap
counts, access the website at (http://www.udel.edu/IPM/traps/latestblt.html)
or call 1-800-345-7544 (in-state); 1-302-831-8851 (out-of-state). Counts are updated on Tuesday and Friday.
Vegetable Crop
Diseases –
Lima
Beans.
24(c) Issued for Ridomil Gold/Copper for downy mildew on lima beans. There is a 24 (c) now in effect for the use of Ridomil Gold/Copper for controlling downy mildew on lima beans in Delaware. Ridomil Gold/Copper is labeled for downy mildew control caused by Phytophthora phaseoli at the rate of 2.0 lb/A. Apply the product prior to disease development or in the early stages of disease. Up to four applications can be made on a 7-10 day schedule. Do not apply within 3 days of harvest. Ridomil Gold/Copper can be alternated with Champ or Kocide as well on a 7-day schedule as well. Coverage is important, so apply in a minimum of 20 to 50 gallons/A. A minimum of 5 gallons/ acre is recommended for aerial application. This new label must be in the possession of the user at the time of application. County agents have copies if needed.
This addition to our fungicide arsenal will be very important this season if weather conditions become very favorable for downy mildew this fall. Ridomil Gold/Copper has been the best product for preventing and keeping downy mildew under control in four years of trials with varying disease conditions. Champ DP, Kocide 2000 and other copper fungicides have been good preventative fungicides for us, are inexpensive, but have no systemic activity. The copper fungicides are very good preventative fungicides for downy mildew for application when conditions are favorable for infection and should be used. Ridomil Gold/Copper will be very useful if downy mildew is detected in a field or when a non-infected field is close to an infected field. Unfortunately neither fungicide will provide any control of white mold, our other important disease of lima beans.
With the importance of lima beans to our processing vegetable industry on the Shore and trying to increase Fordhook-type varieties which are not resistant to races E and F that are present, disease control continues to be an important part of our production practices.
Field Crop Insects
-
Soybeans.
Continue to scout later planted soybeans for soybean aphids
through the end of this week. At this point, the numbers of winged adults in
most fields is very low. It appears that they could still be migrants and do
not appear to be the result of crowding on the plants and movement from the
field. We have not seen any nymphs with wing pads ("alatoid
nymphs"). The good news is that we have only seen or heard reports of
economic levels in 5 fields. Parasite activity has started to increase in some
fields so watch for "mummies" (parasitized aphids) before making a treatment
decision. The widely accepted threshold in the
The potential for podworms still
remains moderate and this will be an important week to scout fields to detect
small podworms. Begin scouting as soon as blossoms
are present for corn earworm (CEW), beet armyworm (BAW) and fall armyworm (FAW).
Low levels of corn earworm (1-2 per 100 sweeps) have been found in all counties
and an occasional BAW and FAW have been found in fields in
Small
Grains.
After this past season, we all know that it is difficult to
predict what will happen with insect populations. Even though the recent
weather has been warm, the overall cooler summer temperatures could result in heavier aphid
populations in small grains this fall, especially in early planted fields. With
delayed plantings of corn and soybeans, most fields will be planted later and
less susceptible to attack; however, early-planted fields should be watched
carefully. Factors that increase the potential of a return from applying an
insecticide to control aphids and to reduce barley yellow dwarf virus (BYDV)
infection in wheat include: (1) normal-cool summer temperatures with adequate
rainfall; (2) intensive wheat management including high fertility; (3) use of
BYD susceptible varieties;
(4) planting before the Hessian fly free date; and (5) a late,
warm fall. We are still using a threshold for fall treatment for aphids (except
greenbug) of 15-25 aphids per foot of row in
combination with a known history of BYDV.
Direct damage from green bug aphid has also been an issue in recent
years. If you are able to scout, be sure you plan to sample your fields at
emergence. Although we do not have any thresholds developed in our area for
green bug, thresholds from
Waiting to plant after the fly-free date (Oct 3 -
Field Crop
Diseases –
Wheat.
I have had some questions about planting seed from possibly scab (head blight) infected fields.
After consulting with Dr. Arv
Grybauskas at the
Be sure to plant treated seed. For loose smut and seed-born scab control, request seed treatment of Raxil/Thiram, Dividend Extreme at the 4 oz/cwt. rate, or Vitavax 200 plus LSP(thiabendazole) at 0.25 fl oz/cwt. They will perform the best for this disease combination. If you want early season powdery mildew control as well, Dividend at the 4 oz. rate will provide that. If scab is not an issue, treat with Baytan 30 plus thiram or captan for early season powdery mildew, loose smut and a reduced level of control of seed born scab.
Grain Marketing Highlights -
The size of this year's corn and soybean
crops are likely to remain unknown until well into harvest. Weather uncertainty
and the impact that prolonged dry spells will have upon eventual yield outcomes
is creating price volatility in commodities trading. This week produced a crop
condition report that declined overall for corn and soybeans, greatly exceeding
trader expectations. The impact from this was a large rally on Tuesday morning,
only to be taken out that afternoon by an isolated thunder storm passing
through
Net wheat export sales hit a marketing year
high for the week ending August 21, at 47.3 million bushels. This level was
more than double the total expected. Corn and soybean sales were also better
than the trade expected. New crop corn sales registered at 37.4 million bushels
for corn and 20.8 million bushels for soybeans Old crop sales tallied at 7.7
million bushels for corn and 1.9 million bushels for soybeans.
Market Strategy.
New crop corn and
soybean sales should be placed on hold this week, assuming 50% of intended
production is already on the books. Commodity traders are likely to trade the
markets both sides of unchanged going into the long holiday weekend. There will
be large interest in next Tuesday's crop condition report. If conditions
decline again, then we could see some added volatility to these markets next
week.
Alfalfa and Potato
Leaf Hopper Injury in 2003 - Richard W. Taylor, Extension Agronomist, rtaylor@udel.edu
and
The 2003 growing season has been a difficult one for alfalfa
producers. Not only has hay making been
very difficult with the frequent rains, but potato leaf hoppers (PLH) have
continued to attack the crop time and time again throughout the summer. Some growers with PLH resistant alfalfa
varieties may have thought that they did not need to worry about the need to
spray for PLH. However, the one thing to remember about alfalfa is that an alfalfa
variety is a population and each seed and resulting seedling is genetically
different. In a PLH resistant variety,
alfalfa plant will express the full range of phenotypes for this particular
trait. Some of the older PLH resistant
varieties only had 25 to 45 percent of the plants that would show
resistance. The very newest varieties
may show 60 to 80 percent resistant plants.
In 2003, researchers working with some of the new so-called 4th
generation indicate that the resistant varieties performed very well. They still had a lot of hoppers in the crop
and some yellowing was visible, but looked great side-by-side a nonglandular-haired variety. The consensus among researchers evaluating
these varieties is that the newer varieties are good, but insecticides may
still be justified under extreme outbreaks.
Unfortunately, economic threshold level for the new PLH-resistant varieties
is not clear at this time.
How much effect will
2 or 3 consecutive cycles or injury from PLH have on a stand of hopper
resistant and non-resistant alfalfa variety?
If an infestation of PLH leads to the typical leafhopper burn that causes a u- or v-shaped lesion to appear at the apex of the alfalfa leaflet (See Photo 1) and that can cause plant stunting, the effects can impact yield from one or more cuttings. This is typically what happens in a moderate to slight infestation season.
Photo 1. Note typical
potato leaf hopper burn on leaflets in the lower left corner of photo (Photo by
R. Taylor).
Photo 2. Typical potato leaf hopper
nymph (Photo by R. Taylor).
In a severe PLH season as we’ve experienced this year, PLH burn may occur in multiple harvest cycles and lead to more significant long-term impacts. Several factors may come into play during repeated PLH infestations that lead to burn symptoms. First, the stunting that often accompanies the more visible leaf burn will reduce the photosynthetic capacity of the plant and reduce crop yields. Secondly, the lack of photosynthetic capacity diminishes the ability of the alfalfa plant to replace the root reserves it needs for the next growth cycle or for winter hardiness. Third, the stunting that often accompanies leaf burn allows germinating weeds to be more competitive against alfalfa. Competing weeds and especially summer annual grasses such as barnyardgrass, giant foxtail, giant crabgrass sometimes called water grass, and fall panicum can rapidly form a canopy over the stunted alfalfa plants further reducing their ability to manufacture food as well as increase the incidence of diseases due to shading, increased canopy humidity, and reduced plant vigor. Fourth, the visible stunting the grower sees is compounded by the fact that root growth can also be reduced. Poor root growth results in less nutrient uptake and less available water. These growth limitations then compound the previous problems the plant experiences.
What does this mean for the grower? On an immediate level, yields can be reduced significantly and crude protein levels of harvested forage will be lower than normal because of the loss of leaf tissue. Often with severe repeated PLH infestations, growers can expect diminished stand survival during periods of drought stress in late summer or during the winter if conditions are harsh. Stand life will be shortened and if the problems are severe enough stands in the year following multiple PLH infestations will be inadequate for maximum economic yield. New stands seeded either the fall before or this past spring will be at most risk but older stands nearing their expected life expectancy are also at severe risk.
What can a grower do
to manage PLH?
First and most critical are new seedings of alfalfa planted either the fall-before or in the spring of the current year. These new seedings must be protected during the first summer’s growth. Pay strict attention to PLH thresholds and control PLH immediately when thresholds are passed. Part of the reason for this is to prevent PLH damage from limiting root growth during this important establishment phase and to ensure good root reserve development before the critical winter period. Growers should also limit the food supply of PLH by making a short, clean cut and harvesting the entire field at one time. Cutting an entire field cleanly at one time will eliminate at least temporarily the presence of PLH nymphs and cause the surviving adults to disperse to other fields. Generally, PLH populations tend to drop dramatically after a cutting and won’t begin to rebuild until about 10 to 15 days of regrowth is present in the field. Again, do not depend on averages but continue scouting to be sure PLH populations do not reach the threshold level. Another option is cutting slightly early and using 4 to 5 cutting cycles rather than 3 to 4 as this will limit the time during which PLH populations can buildup.
Human nature can come into play as well. Growers should avoid revenge sprays and should not spray alfalfa stubble until thresholds are exceeded. You should always plant alfalfa varieties that have good performance records even under heavy PLH pressure. Also, growers should adjust their action PLH thresholds based on crop conditions. In years where weather or other stresses may be unfavorable for rapid alfalfa growth, you should adjust thresholds downward to help protect the health of the stand and increase the frequency with which you monitor PLH levels.
2003
Extension Agronomist, rtaylor@udel.edu
Crop consultants and others interested in continuing education credits for CEU’s for Certified Crop Adviser, Nutrient Management Programs, or Pesticide Recertification can now register on-line for the 2003 Mid-Atlantic Crop Management School to be held at the Princess Royale Oceanfront Hotel and Conference Center in Ocean City, MD on November 18 to 20, 2003. To register on-line you only need a major credit card and access to the internet. The URL address for on-line registration is as follows:
https://crayola.hcs.udel.edu/conf/registration/crop_management/
If you would like a copy of the printed brochure or have not yet received one in the mail or your mailing address has changed during the past year, please call me at 302-831-1383 and leave a message with your name, the spelling of your name, your street or postal address, and a return phone number. I will send you a brochure immediately.
If you would like to view the brochure on-line before registering and do not want to wait for a mailed copy, go to the following URL web site compliments of Tom Basden at West Virginia University:
http://www.wvu.edu/~agexten/temp/Cropmanschl.pdf
|
http://www.rec.udel.edu/TopLevel/Weather.htm |
Weeks of August 21 to
|
|
Rainfall: |
|
0.07 inches: August 22 0.13 inches: August 26 0.80 inches: August 27 |
|
|
|
Air Temperature: |
|
Highs Ranged from 91°F on
August 22 to 77°F on August 24. |
|
Lows Ranged from 71°F on
August 22 to 54°F on August 25. |
|
Soil Temperature: |
|
77°F average for the week. |
|
(Soil temperature taken at
a 2 inch depth, under sod) |
Web Address for the U of D
Compiled and Edited
By:
Cooperative Extension Education in Agriculture
and Home Economics, University of Delaware, Delaware State University and the
United States Department of Agriculture cooperating,