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ISSUE 6   June 14, 2007

FLEA BEETLES ON CANOLA

A small proportion of canola fields needed to be sprayed to control flea beetles in the Northeast Region of North Dakota. The situation was probably caused by the cooler weather, which extended the flea beetle feeding activity; and at the same time, the reduced residual of seed treatment products in the early-planted canola (beyond the 25 days after seeding protection window). Canola should be able to outgrow the flea beetle feeding injury in most situations.

 

CUTWORM FEEDING CONTINUES

Reports of cutworm damage, especially on sunflower, continue to come in this season. Early season cutworms, like Dingy cutworm should be near the end of the their larval development (=feeding injury stage) and getting ready to pupate (resting stage). However, late season cutworms, like Red-backed cutworms are still completing their larval development and will reach a length of 1.5 inches long. So, continue to be vigilant in scouting for cutworms.

 

ALFALFA PRE-HARVEST INTERVALS FOR CONTROL OF ALFALFA WEEVIL

There has been some question on what to spray on alfalfa for control of alfalfa weevil when treatment is necessary and close to cutting. Here’s a summary of the pre-harvest intervals for the insecticides labeled in North Dakota:

Insecticide

Preharvest Interval (days)

Permethrin or Ambush

14

Baythroid XL

7

Tombstone

7

Sevin

7

Lorsban 4E, Yuma 4E, or Warhawk

7 (˝ pt per acre rate);
14 (1 pt per acre rate)

Furadan 4F

7 (0.25 lb per acre rate);
14 (0.5 lb per acre rate)

Imidan 50 WP

7

Lannate LV

0

Malathion 57EC

No time limitation

Methyl parathion

15

Methoxychlor 2EC

7

Mustang Max

3

Proaxis

1 day for forage and
7 days for hay

Warrior or Taiga Z

1 day for forage and
7 days for hay

Steward EC

7

Respect

3

 

LOW POPULATIONS OF CEREAL APHIDS COMMON

Cereal aphids are common, especially in eastern half of North Dakota (see IPM wheat/barley maps). Fortunately, most of the reports indicate a low percentage of infested stems (<25%). Scout during the stem elongation to flag leaf stage. Use a treatment threshold of 80-85% of stems with at least one aphid or more and treat prior to complete heading. Spraying insecticide at or after heading isn’t recommended because of the low economic returns. If aphid populations are very high, a treatment at heading may be justified.

Aphids in Barley map            Aphids in Wheat map

Can we wait to spray for aphid with a later fungicide application for scab? A good article is reprinted here from Red River IPM (I. MacRae) for your information:

"This depends largely on how long the wait is……. If it’s a later-planted fields (i.e. still in 6-leaf stage) that are up to 2 weeks from fungicide treatment, then there might be a greater potential for yield loss if aphid numbers are already/near threshold. Aphids damage plants by sucking sap, so yield loss depends not only to how many aphids are on the plant, but how long they’ve been there. Entomologists use the concept of cumulative aphid days (CAD) –– 20 aphids on a plant for 1 day = 20 CAD, 20 aphids on a plant for 5 days = 100 CAD, and so on. The concept was borrowed from heat unit calculations. Yield loss in cereals from aphid feeding has been estimated at approximately 0.6 bu/ac/100CAD. Potential minimum yield loss can then easily be calculated by calculating the average number of aphids per stem and multiplying by the length of the wait. I say the potential minimum yield loss because if 6-leaf plants are already at threshold, the aphid populations will likely increase over the next 2 weeks.

Total CAD isn’t the whole story, however. The rate of yield loss decreases as the plant matures. There are a number of reasons: physiological changes in the plant and maturation of the grain make it less susceptible to aphid damage, after heading the plant starts to become less suitable as a host, aphid populations start to decline, and natural mortality factors, such as predators, start to impact the population so that aphid populations generally start to decline within 2 weeks after heading. From heading on, there usually isn’t enough time to accumulate sufficient aphid days to cause the amount of yield loss that would economically justify an insecticide application.

Data suggests that the way CAD accumulate also influences the amount of resulting yield loss. Lower populations of bird-cherry oat aphids that fed over a longer period caused greater yield loss than did higher populations feeding for a short period even though the CAD were about the same. So, generally speaking: the longer they feed, the more damage they do…

The Bottom Line –– Just keep an eye on the populations for now and see what happens, don’t treat before threshold, and don’t wait for fungicide application at heading if you’re at threshold now."

 

NO SOYBEAN APHIDS YET!

It is still early in the season and too difficult to determine if soybean aphids will become a major insect pest problem this year. So far, no soybean aphids have been detected in North Dakota. With the strong southernly winds, it looks like migrants may be the main threat for the 2007 soybean crop. Reports from Minnesota indicate low numbers of aphids observed on the early planted fields in southern Minnesota. If you find any soybean aphids, drop me a note.

Janet Knodel
Extension Entomologist
Janet.Knodel@ndsu.edu

 

POTATO LEAFHOPPERS IN ALFALFA

Potato leafhoppers have been reported at high levels in southern Minnesota; therefore, it is time to start scouting for leafhoppers. The primary area of concern is the newly clear-seeded stands. Early infestation can cause serious damage to seedling stands. Generally, 1-year-old or older stands can be harvested at normal maturity and avoid economic damage in this area. However, new seedings are exposed to the leafhoppers for a longer period of time, upto 70 to 80 days, before the first harvest will occur. If significant infestions occur, leafhoppers will literally stop the growth of the seedings with hopper burn, V-shaped yellowing of the leaf tip.

Potato leafhoppers have rarely done significant damage to producing fields in this area. Saying that, producers in Ohio, Indiana, Illinois, and other states in the eastern Midwest must spray to control potato leafhoppers if they do not use a good leafhopper resistant variety. Likewise, southern Minnesota has had problems on second growth alfalfa.

Generally, potato leafhopper damage is most severe in North Dakota on second-growth seeding-year alfalfa. But, if the leafhoppers arrive earlier than usual, they can do damage to first crop, so begin scouting the newly seeded alfalfa fields that are clear seeded. Seeding with a companion crop generally reduced the problem in North Dakota, but very heavy infestations like they get in Ohio will cause serious damage to companion crop seeding also.

Dwain Meyer
NDSU Plant Science
dwain.meyer@ndsu.edu

 

EPA APPROVES INSECTICIDE FOR GRASSHOPPER CONTROL IN FLAX

The U.S. Environmental Protection Agency has issued a Section 18 exemption for Mustang Max (zeta-cypermethrin, FMC Corp.), allowing North Dakota flax producers to use the insecticide for grasshopper control.

"I asked the EPA to reissue this exemption, because drought conditions in late 2006 created ideal conditions for above-normal grasshopper populations this year," said Agriculture Commissioner Roger Johnson. "Flax is a later season crop; it is green and attractive to adult hoppers, when they move away from ripening small grains and other drying crops and grasses. Left uncontrolled, high grasshopper populations can decimate a flax crop."

The exemption allows ground or aerial applications at a rate of 2.8 to 4 fluid ounces of product per acre. A maximum of 8 fluid ounces per acre is allowed for the season. A maximum of 210,000 acres of flax may be treated. The exemption is effective immediately and expires Sept. 30, 2007.

Jim Gray
North Dakota Department of Agriculture


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