Volume 10, Issue 24 September 6, 2002
Volume 10, Issue 24 September 6, 2002
At this point, we can find corn
earworm and beet armyworm in just about any crop that is green. The list of
crops damaged expands each day to include soybeans, sorghum, alfalfa, forage
grasses, fruit and most fall vegetables. I have probably left one out so if it
is green -- especially after the rain -- be sure to look for "worm
damage". In forages and turfgrass, we are also finding economic levels of
fall armyworm and true armyworm so be sure to check all crops carefully to
detect problems while the worms are small and before significant damage has
occurred.
Vegetables
Vegetable Insects
-
In general, beet
armyworm can still be found in many crops. In addition to cabbage, beans, and
peppers, they have been found feeding on watermelon fruit, pumpkins, cucumbers,
and apple leaves. The pyrethroids have provided poor
control -- even at higher rates. Lannate, Larvin and Orthene have also
provided poor control. In many cases, Spintor is
labeled on a wide variety of crops and will provide good control. Where Avaunt and Confirm are labeled, they will also provide good
control.
Cabbage.
Continue to scout for diamondback (DBM), cabbage looper (CL) and beet armyworm (BAW). If DBM and CL are both 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 or Confirm (8 oz/acre) will also provide control. If beet armyworm is the predominant, Avaunt, Confirm or Spintor should be used.
Cucurbits.
High beet armyworm populations have been found in a few
cucumber fields in
Lima
Beans.
Be sure to continue to sample fields carefully for corn earworm, beet armyworm, lygus and stinkbugs. A treatment should be applied if you find one corn earworm per 6 foot of row or 15 tarnished plant bugs and/or stinkbugs per 50 sweeps. Since corn earworm populations are high and moths are readily attracted to blooming fields, multiple applications may be needed to achieve control. Also, if Lannate is used, be sure to use the high rate of 2-3 pts/acre if mixed larval sizes are present at treatment time.
Peppers.
At the present time, all peppers should be sprayed on a 5 to 7-day schedule for corn borer, corn earworm, and beet armyworm control.
Snap
Beans.
Processing snap beans in all areas of the state should be treated at the bud and pin stages for corn borer control. Orthene or Address should be used at the bud and/or pin stages for corn borer control. In all areas, a pyrethroid should be combined with Orthene at the pin spray for earworm control. After the pin stage, sprays will be needed on a 5-day schedule from the pin spray 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). You should treat fresh market snap beans for corn borers, corn earworm and beet armyworm on a 5-day schedule from the pin stage until harvest.
Spinach.
As soon as plants emerge, be sure to scout for beet armyworm and webworms. Controls should be applied when worms are small and before they have moved deep into the hearts of the plants. Since Lannate cannot be applied before plants are 3-inches in diameter and it only provides control of small larvae, Confirm or Spintor will be needed for beet armyworm control. If webworms are the predominant species, Ambush, Pounce, Confirm (6-8 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 in all areas of the state. Since corn earworm catches continue to be high and fall armyworm can be found in silk stage corn, you should consider combining Lannate LV at 1.5 pt/A with the highest rate of a pyrethroid. 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 ) .
Vegetable Diseases
-
Snap
Beans and Sweet Corn.
Be on the lookout for snapbean rust in fall plantings. When it is first observed apply chlorothalonil (Bravo, Equus, Echo) or Nova and repeat every 7 days.
Rust can be a problem in late sweet corn as well. Keep scouting fields and look at the lower leaves of small plants. If infected plants are in the whorl stage or younger, apply a fungicide and repeat every 7-14 days depending on the product. Apply Tilt, Quadris, mancozeb or chlorothalonil.
Lima beans.
We have not seen any downy mildew (figure 2) yet, but we have seen Phytophthora pod rot (figure 1) caused by Phytophthora capsici in a field of irrigated limas. Now is the time to be thinking about applications of 2 lbs./A of Champ DP or Kocide 2000 for the control of downy. Prevention is the best control rather than waiting to see the disease. Pythium pod rot is also present in fields that have good vine growth and lots of rain. Pythium causes very fuzzy looking white fungus growth on the pods and sometimes leaves that are touching the ground. Copper fungicides applied for downy mildew might provide some control of Pythium otherwise there are no chemical controls.
Figure 1. Phytophthora Pod Rot Figure 2. Downy Mildew
Phytophthora capsici only infects Downy mildew will be seen on pods,
lima bean pods petioles, and flower stalks (racemes).
Field Crop Insects
-
Please read alert on page 1.
Soybeans.
Continue to sample soybeans for corn earworm and beet armyworm. We can find all sizes of larvae indicating a new hatch before the rain. Usually, we don't encounter a lot of small corn earworms or new infestations in September. However, at this point we are seeing new larvae so you will need to continue scouting fields, especially those that are flowering and trying to set and fill pods. Although economic levels of both continue to be found throughout the state, it will be important that you time treatments to avoid the need for multiple applications. When possible, try to wait until 1/3 of the populations is 3/8-inch long before treating. With the recent rains, cool evenings and warm days, we should start to see diseases attacking corn earworms. Be sure to watch for diseased worms before making a treatment decision. In addition, corn earworm will begin to enter their diapausing (overwintering) stage at the end of September so do not treat too quickly. If you feel you have not gotten the best control after spraying, be sure to get a worm sample to me or your county agent. We may have a mixed population of corn earworm (Helicoverpa zea) and tobacco budworm (Heliothis virescens) which comes from the south and is much tougher to kill.
In comparison, the beet armyworm is a more tropical insect so only a killing frost will really reduce populations. We are not sure if the same fungal pathogens will attack them so be sure to continue to sample carefully for beet armyworms. We are seeing a second hatch of small larvae this week and defoliation has increased in many fields. We have also found beet armyworm in soybeans in all three counties. Steward has worked very well on mixed populations and fairly large beet armyworms. Although it was not clear how well the Lorsban worked last week, we did another field scale trial on Tuesday. A quick evaluation at one day after treatment indicated that it may have done a good job on beet armyworm. It was applied by air at 2 pts/acre of product and 5 gallons of water/acre. We will do a more detailed evaluation on Friday and let you know how it worked. Last week, Lorsban did not appear to work very well on corn earworm so we are not sure it will be the product of choice if mixed populations are present. We are still getting mixed reports on how well Larvin has performed against beet armyworm.
Forages and Small Grains.
As indicated above, economic levels of corn earworm (CEW),
beet armyworm (BAW) , fall armyworm (FAW) and true
armyworm (AW) have been found defoliating alfalfa and forages grasses in
We are limited in our control options for these crops. Chemical selection will depend on the crop and insect species present. There are a number of products labeled for pure stands of alfalfa including Steward, Lorsban, Lannate, Baythroid, Warrior, Mustang, Ambush and Pounce. Steward has given excellent control of CEW and BAW in soybeans, but the lowest labeled rate on alfalfa is 9.2 ounces per acre. Unfortunately, we have no experience with FAW and AW. The Lorsban label claims AW control so it should work on AW and FAW. Our recent trial in soybeans suggests it should work on BAW, but at this point appears weak on CEW, which is not on the label. We used 2 pt/A which has a 21 day wait until harvest. Lannate should work on FAW and AW but has given variable control this season of BAW. It works on CEW in other crops; however, it is not on the alfalfa label. As far as the pyrethroids (Ambush, Baythroid, Mustang, Pounce and Warrior), they are all labeled for different combinations of insects. BAW has been poor with the pyrethroids this year and certain labels state control of only first and second instar (small) FAW. So, be sure to read the label for rates, use directions, days to harvest and insects controlled.
There are very few labeled options for mixed stands of alfalfa or forage grasses. At this point, only Sevin has a label on alfalfa, pastures and grasses grown for seed. It should provide only fair control of very small CEW, FAW and AW larvae. It will not control BAW. Lannate is labeled on bermudagrass pastures for armyworms, it so should control both FAW and AW, but has been variable on BAW this season.
Also, as you make plans to plant small grains, you will need
to consider potential armyworm damage. In
Wheat
and Barley.
As far as aphid management, we did see a few locations with
barley yellow dwarf this past spring. More importantly, we did have high
numbers of green bug aphid mainly in barley and early planted wheat. Although
this aphid can transmit barley yellow dwarf, the greatest problems occur with
direct plant damage. Unlike other aphids, this aphid injects a toxin into
plants, which shuts down plant growth. Entire
sections of fields were killed in
Grain Marketing Highlights -
Commodity Prices Rebound Sharply
Monthly average '02
The corn, soybean, and wheat pits remain in a positive mode
as we enter harvest. Harvest has gotten underway in the Southwest and
Southeast, and is rapidly approaching throughout scattered portions of the corn belt. Hot/dry
weather, although stated to be a disappearing factor, is still taking its toll
on potential
Marketing Strategy
Basis bids in Southern Delaware are currently 35 over for
new crop corn and 5 over for new crop soybeans (likely to vary depending upon
the delivery point). New crop corn sales currently equate to $3.15 per bushel.
New crop soybean sales currently equate to $5.61 per bushel. The market for
corn, wheat, and soybeans is currently in a positive mode, with resistance for
Dec. corn at $2.81 and resistance for Nov. soybeans at $5.56 per bushel.
Field Crop
Diseases -
Soybeans.
Several diseases have been seen this week. Charcoal rot mentioned previously is favored by dry weather and continues to be seen. Usually irregularly sized patches of infected dying plants are seen in the field, but this year as in 1999 we are seeing individual plants in the row infected and dead or dying. When this happens you see scattered plants dying either singly or several in a row flanked by healthy ones. Carefully dig up plants and look at the roots and lower stem. They will often be gray and if you scrape the gray lower stem or roots you can see many small black flecks that look like the tissue was covered with powdered charcoal. Often if the plants are dead and you split the stems, the pith is full of these tiny microsclerotia as well. Rotation will help to some degree as well as planting later maturing varieties.
The other disease that was seen is stem canker. Stem canker causes wilting and death of scattered plants and when severe large areas are infected. Reddish-brown lesions develop first near the mid-stem nodes of infected plants from mid-season to maturity. Later the lesions turn dark, girdle the stem, and kill the plant. The tissue above and below the infected area remains green. Select tolerant varieties and rotate for control.
Forage Stand Evaluations Following Severe
Stress Conditions – Part I
Richard W. Taylor,Extension Agronomist, rtaylor@udel.edu
Many pasture and hay
fields have either been injured with plant density reductions or have been
forced into dormancy during the long dry spell this summer. The significant rainfall this past week has
helped these fields begin regrowth. Once green-up occurs, you will need to
evaluate these fields to see if renovation will be needed. Last week, I said I would offer some
guidelines for evaluating your fields.
I’m still researching the problem so I’m not ready to give numbers of tillers
per square foot or plants per square foot yet.
While you wait for
me to develop those guidelines, you will need to walk across your pasture or
hay fields and determine how many plants or tillers per square foot you
have. To do an evaluation, make a 1-,
2-, or 4-ft2 rectangle or square from wire or wood, walk across the
field dropping the rectangle or square at random, count the number of tillers
or live plants of your dominant grass species enclosed by your device, keep a
running total, and after taking about 10 to 20 counts divide the total by the
number of counts and that number by the number of square feet represented by
the device. This will give you an
estimate of the number of plants/tillers per square foot. Be sure to decide ahead of time how you’ll do
the counts. From what I’ve seen to date,
you would be counting the number of tillers in Kentucky bluegrass, smooth bromegrass, and reed canarygrass
pasture or hay fields and counting plants in orchardgrass,
tall fescue, timothy, and ryegrass fields.
I understand from
our entomologist, Joanne Whalen, that various foliage feeders are attacking
forages aggressively at this time. For
fields that were nearly dead and are trying to recover by sending up new shoots
or tillers, it will be important to try to protect this new vegetation since it
is the only photosynthetically active tissue
available to the plant and the plant’s food reserves are probably very
low. Food reserves must be reestablished
by late fall for the crop to survive the winter. Contact your pesticide dealer for information
on products that can be used to control damaging insects and be sure to follow
all label warnings and restrictions.
Another suggestion
would be to fertilize grass field regrowth with
nitrogen to stimulate a more rapid recovery.
Finally, weed encroachment may have become an important problem with the
severe stress conditions the pasture experienced this year, so be sure to read
the accompanying article on pasture weed control in this issue.
Weed Management in Pastures - Quintin Johnson, Extension Associate, Weed Science, quintin@udel.edu , Richard W. Taylor,Extension Agronomist,