SW MN IPM Stuff 2016 Issue 4

Volume 19, Issue 4 - May 5, 2016

This newsletter is available in a print-friendly pdf format: SW MN IPM STUFF 2016-04

This newsletter and the advice herein are free. You usually get what you pay for.

Crop weather

Rainfall, air and soil temperatures, degree-days, soil moistures, and other current and historical weather data for the University Southwest Research and Outreach Center (SWROC), a little spot about two miles west of Lamberton, MN can be found at the SWROC weather webpage.

Corn planted the week of April 11 has emerged. Short-term submersion did not seem to impact stands, and cool temperatures likely helped survival in a temporarily aquatic habitat. Areas under water for a prolonged period may be different. If not managed, wet areas with poor emergence or left unplanted can see increases in the weed seed bank. 

emerging soybeansTo provide training material for an annual school for hail adjusters, Steve Quiring always tries have some short maturity soybeans planted early at the SWROC. These soybeans were planted on April 15 are beginning to emerge. They are looking good in spite of the cold and wet conditions.

It looks like we will have a few days of good weather before more rain in the unfortunate forecast for next week. Growers started getting back into area fields on May 4th, but some are still too wet for field work. It will be a busy weekend.

Wheat & etc.

Aphids - check winter wheat now

aphids on small grain

English grain and bird cherry-oat colonies on rye leaf. The 85% stems infested action threshold accounts for infestations of cereals by multiple species. The smaller, dark, bird cherry-oat aphid often colonizes leaf sheaths at the base of the plant.

Include aphids in your wheat, barley and oat scouting plans this season. For those of you who read last week's issue and my hope for cool, wet weather slowing aphid populations, the chronic disappointment is why I am seldom optimistic.

Both bird cherry-oat and English grain aphids have increased dramatically in SW Minnesota the past week. This is the most dramatic early-season infestation I have observed in 19 years at the UMN SWROC. Winter wheat populations reached the treatment threshold of 85% of the stems infested, and we are treating variety trials at the SWROC. This does not mean all fields or areas have high aphid populations.

Aphids have started to move to 1-2 leaf spring planted grains, but at this point, I am finding aphids mostly on oats planted near winter wheat, barley and rye. These two species also colonize corn later in the season. Based on this spring's weather patterns, SW and SC MN are most likely to have received large numbers on immigrant aphids. However, alate (winged) aphids are now being produced and can be expected to move to new areas. 

Results of assays by Dr. Madeleine Smith, U of MN Plant Pathology found English grain aphid migrants were carrying barley yellow dwarf virus (BYDV) but at a low percentage. We are sending additional aphids, particularly bird cherry-oat, for assay.

BYDV cannot survive without live plant tissue or infect new plants without an aphid vector. Aphids must acquire the virus by feeding on infected plants. After a several hour latent period, during which the BYDV virus particles circulate through the aphids body and into the glands that produce saliva, the aphid can transmit the virus to new plants. The virus does not increase inside the aphid, but the virus particles can persist within the aphid for a period of several days. This allows migrating aphids to bring the virus into new areas. The disease is more severe when plants are infected while small.

However, at this point, we do not have evidence of a large percentage of aphids carrying BYDV, and there is no reason to adjust economic thresholds.

Black cutworm

Larvae from the March 28 and April 12 flight should be large enough to produce visible leaf feeding and in the case of March 28 flight be large enough to cut small corn by May 16. Areas of southern Minnesota are at risk for stand loss from black cutworm larvae. See the UMN black cutworm reporting network for the latest newsletters with predictions and articles on black cutworm biology and scouting advice.

Some light reading

This is an educational article on how growth regulator herbicides work. Herbicide physiology is not all that exciting to this amateur entomologist. While likely to be less entertaining than the new Captain America movie, these Australian weed scientists are very good at explaining things and making the subject interesting: AHRI: How stuff works: 2,4-D.

Production agriculture events at the SWROC

There will be a training for agricultural producers at the U of MN SWROC on Monday, July 11th. Details to follow.

Happy trails,

Bruce Potter