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Be on the watch for spider mites if weather turns hot, dry

By Janet Kubat Willette
jkubat@agrinews.com

Date Modified: 07/24/2013 4:23 PM

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LE CENTER, Minn. – Weed control is the issue of the moment for corn and soybeans producers.

Pre-emergence herbicide for soybeans worked well this year, said Extension educator Dave Nicolai, speaking at a field day Friday in Le Sueur County. It gave early season weed control and helped avoid the multiple weed flushes and variety of weed sizes that growers who didn't apply pre-emerge products experienced.

Soybean aphids aren't yet a significant problem, but farmers should be on the lookout. It doesn't make sense to spray to prevent aphids because spraying knocks out the beneficial pests that work against aphids, Nicolai said. Scout and spray when it's right for the field.

Also, be on the watch for spider mites. If hot, dry conditions develop potential exits for spider mites.

Corn has made good progress with the recent warm days and nights and Nicolai expects tassels to begin appearing this week. Timely rain will be essential as the crop continues to progress.

Rainfall is especially needed in southwestern Minnesota, where the previous two years have brought drought conditions in the summer. In central and southeast Minnesota, root depth is an issue because of excessive early season moisture.

Southeast Minnesota has the most challenged crops, said Nicolai, who crisscrossed the state last week for field days. An estimated 30 percent of the acres in southeast Minnesota haven't been planted, according to information from Extension.

What was planted got in late and corn stands tend to be uneven. Soybeans are short.

From Interstate 35 to Highway 169, it's a transition zone, with some prevented plant acres and some nice-looking crops.

West of Highway 4, crops look much better, Nicolai said.

Prevented plant

Producers who weren't able to plant this spring and who chose the prevent plant option for crop insurance have their own challenges. Weeds have overtaken the fields and many farmers have knocked the weeds down.

Extension recommends farmers mow or chop larger weeds at this point because it will destroy the most plant biomass and it won't expose the soil to wind and water erosion. If a cover crop is to be planted, mowing or chopping will need to be done before seedbed preparation begins.

"We want them to control the weeds," Nicolai said.

Giant ragweed can produce 10,000 seeds; common water hemp 70,000; and waterhemp 100,000 if left untended, writes Extension agronomist Jeff Gunsolus. A larger seed bank will make weed management more challenging next year, he continued.

If soil is left bare, the risk of soil erosion and fallow syndrome increases. Fallow syndrome results when there is no plant growth in an area for an extended period of time, write Extension educators Liz Stahl and Jill Sackett. Populations of good fungi in the soil are reduced because this type of fungi needs active roots to survive.

A cover crop can't be harvested until after Nov. 1. Extension offers a variety of resources to choose the right crop.

Figure out what you want from the cover crop and then find the crops to fill that void, said Extension educator Doug Holen.

In Minnesota, farmers may plant annual, biennial or perennial grasses and legumes on prevented plant acres. They may also plant a mix of corn and soybeans. No straight seeding of corn or soybeans is allowed.

It's too late to plant cool-season grasses, Holen said. Instead, farmers should switch to warm-season grasses.

NRCS cover crops recommended for planting in July include flax, winter triticale and spring wheat. In August, winter barley, canola and field or winter peas should be sown.

Crop options exist that will yield terrific tonnage in a short period of time. Foxtail millet meets that description, maturing in 50 to 55 days, Holen said.

Another option is for producers to fall seed alfalfa in late summer for harvest next year.

Farmers who have highly erodible land or a conservation plan must plant a cover crop. Check with the Farm Service Agency and your crop insurance agent about what the requirements are for your fields.

If farmers want to plant winter wheat on the acres for harvest next year, Holen recommends they wait until late September. If producers just want to harvest it for forage in the fall, it's OK to seed earlier.

Forage is in short supply. Nicolai said he's never seen as much harvesting of ditch hay as he's seen this summer between Lamberton and Le Center.

Wheat situation

Little spring wheat was planted in southern Minnesota this year and much of the winter wheat was tilled under because of dismal winter survival rates.

A spring wheat plot planned for the Hoefs farm near Le Center was nixed because the first available planting date was too late. The date was May 11. That date can work, but a grower assumes a lot of risk when planting spring wheat that late, Holen said.

Further north, spring wheat was planted timely and looks good, he said.

Holen said he prefers winter wheat for southern Minnesota because the extra three weeks of growing time in the fall and three weeks in the spring give the crop a yield boost. Winter wheat can yield 85 to 110 bushels per acre in Le Sueur County.

An earlier flowering season usually helps winter wheat to avoid scab. This year, however, the winter wheat on the Hoefs farm west of Montgomery is infected with scab.

It's the first case of scab reported this year. It's actually been a boring wheat pest year, Holen said.

It's too late to do anything about scab, but wheat producers need to know it's there. A grant from the Minnesota Association of Wheat Growers funds the scouting of wheat fields.

Researchers are also studying winter survival rates in the wheat plot. The winter survival rating on the 27 varieties ranged from 3 percent to 97 percent, Holen said. He recommends producers replace anything with a less than 50 percent survival rate. Anything higher than 50 percent will compensate.