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Timing, varieties matter when it comes to herbicides

Staff Writer

HARBESON, Del. (June 21, 2016) — “A number of new products are coming out” in the agricultural herbicide area, Dr. Mark J. VanGessel, professor and Extension weed science specialist based in Georgetown, told attendees at a recent Small Grains Field Day on the Warrington Irrigation Research Farm His research seeks to understand situations where these new chemicals best fit.
Glory (metribuzin) was introduced a few years ago for ALS-resistant chickweed and was tested before being labeled. Some wheat varieties are more susceptible to damage than others, and timing of application matters.
The variety Shirley, for example, is more sensitive to fall applications, with yield losses resulting. When Glory is applied at green-up, however, there was no loss. The best time for application is “a narrow window in early spring,” he said.
Zidua and Anthem Flex both contain pyroxasulfone. They can be applied at an early post-emergence stage on wheat to control annual grasses and small-seeded broadleaf weeds. “A rule of thumb for when to apply them is if you can see the rows, go,” VanGessel said. “If you wait, and the weeds emerge, these products will not control emerged weeds.” These products are fair to good on ryegrass, not good on henbit, but okay on chickweed and bluegrass, VanGessel reported.
The biggest caveat, he said, is that you must plant the seed at least ¾ of an inch deep with a drill.  As a result these herbicides do not fit well with the those fields that have the seed spun on and lightly incorporated.
Sharpen (saflufenacil) can be used preplant or preemergence in wheat and barley burndown for glyphosate-resistant marestail.
VanGessel and his team have looked at three products with HPPD-inhibiting herbicides. Huskie (pyrasulfotole+bromoxynil) is labeled (for annual broadleaf weeds).  Another is coming from Dow AgroSciences and another from Syngenta for corn. “All look very safe on wheat,” VanGessel said. “Huskie has good control of henbit.”
VanGessel suggested “we need to think about fall applications where we have problems — late November or early December. The weeds are too large if we wait until spring. However, timing of fall application depends on when the wheat is planted.”
He reported seeing more annual bluegrass this year than previously in conventionally-tilled fields. Zidua, Anthem and Axiom provide good control. In addition, PowerFlex (pyroxsulam) and Osprey (mesosulfuron) were good when applied in the fall, but not in spring.
With newer products, VanGessel warned, watch for crop rotation restrictions, especially with vegetables.
As always, follow label directions..
Weed identification
VanGessel spoke again later on IPM. He examined 61 fields in fall and spring for weeds after herbicide applications and identified 38 different weed species.
Henbit was the most common; No. 2 was chickweed and third was annual bluegrass, followed by field pansy, johnny jump-up and speedwell.
“On average, there were five to eight different weed species per field. No one product treated them all. It is important to match the right herbicide for your field. In four fields, there were more than a dozen kinds of weeds.”
VanGessel found the number of weeds was higher in fall. In spring, every field had acceptable weed control.
“We hope to have an online resource soon to identify weeds,” VanGessel said. He credited Barbara Scott with having taken pictures for the project. “Winter annual weeds are difficult to identify when they are small,” he added.
A beta version of the resource should be available this fall.
Dr. Nathan Kleczewski, Extension field crops plant pathologist at the University of Delaware, discussed diseases in wheat, among them rust diseases. Rust does not overwinter here but blows up from the south, he said. Stripe rust likes it really cool, so this spring was conducive to its growth. It produces a lot of spores quickly with the right host.
“If you learn it’s in the region, go look!” he insisted.
In variety trials he is conducting, Kleczewski is is learning some varieties are not susceptible to rusts and some are very susceptible.
Literature is available from Extension offices to help identify various wheat diseases.
Powdery mildew is particularly bad this year in some varieties because of the prolonged, cool spring. Kleczewski said the disease has figured out how to get around the gene that carries resistance (in some varieties) to our kind of powdery mildew.
Glume blotch, he said, comes from wheat residue, is dispersed by rain, and moves slowly up the plant. Once high enough on the plant, it makes spores. When the glume is affected, yield loss results.
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Philip Sylvester Kent County agriculture agent, is leading research on the profitability and timing of fungicide use. Sylvester said, “We are seeing more foliar disease this year. Leaf blotch diseases moved in early. The traditional program is to spray at flag leaf. We are seeing instead a solo application at flowering. We have not assessed the spray programs yet,” Sylvester said.
Questions he hopes his research will answer include whether fungicide can be profitable in the Mid-Atlantic region, whether the new programs are better than old practices, whether some fungicides work better than others.
This is the second year of a two-year study, this year involving seven sites from Virginia to Pennsylvania that will test a range of conditions.
Thirteen treatments are being studied on the Warrington Farm, including such products as Tilt, Quilt Xcel, Priaxor and Stratego.
Joanne Whalen, Extension specialist state program leader, and Extension Associate Bill Cissel discussed insects at the field day.
“Farmers need to know how to identify aphids,” Whalen said. Aphids can be vectors of yellow dwarf virus. English grain aphid can be in the heads of grain — look for the actual aphid. Whalen said it is past time to treat for aphids this year, but they are something to keep in mind for next year.
A new aphid has been seen in South Carolina, Sipha maydis, a black aphid which is called the “hedgehog” aphid because its spiny exoskeleton gives the appearance of a tiny hedgehog. Cereal leaf beetle has been seen in hot spots through the state. What farmers should look for — in mid-May — are the eggs.
Virginia’s Eastern Shore is really being attacked by armyworms. It is critical to look for armyworms starting in late April. Examine fields for clipped heads and larvae throughout the field.
Armyworms are leaf eaters but like to clip heads. Keep looking! They hide under debris and weeds during the day and feed at night. Check for small armyworms curled in a C-shape at the base of plants or under debris and weeds. Armyworm frass or droppings also may be found on the soil surface.
Stink bugs can start in wheat fields and move to corn. Stink bugs are rarely an economic problem in wheat. “It takes a lot to harm wheat,” Whalen said. “There’s not an economic impact unless you’re a seed grower.”
Spraying wheat does not affect stink bugs enough to keep them out of corn. They move in and out of the field, Whalen said. Growers should be looking for them in corn. The best time to treat is five to seven days after wheat harvest.
The native brown stink bug, not the brown marmorated stink bug, is the problem pest.
Cissel elaborated on barley yellow dwarf virus. There are four aphids that vector BYDV in Delaware. Bird cherry-oat aphids are the worst. The others are English grain aphids, greenbug aphids and corn leaf aphids.
In a three-year study, researchers are sampling 30 fields weekly until December for aphids. Sampling requires lying on the ground to count the number of aphids per foot row, then identifying the species, Cissel said. “In the previous two years, we have not seen numbers bad enough, but last year’s warm fall favored continued reproduction by aphids. Thirty-four percent of fields reached threshold.” That meant nine or ten fields across the state. Eight fields were found to have BYDV. “We flagged spots to hand harvest,” Cissel added.
The first line of defense is variety selection. Second is insecticide seed treatment. Third is scouting.