Lionel Olson
Extension Agent/Grand Forks County

Soybean aphids have been reported in the county, populations are well below the economic threshold levels thus far.  Now is the time to be scouting soybean fields.  The current recommended threshold for late vegetative through R5 stages is 250 aphids per plant (field average) on 80% of the plants and increasing aphid populations.  Scout 20-30 plants per field and cover at least 80% of the field. To determine if populations are actively increasing, check field over several visits. This threshold provides a 7-day lead time between scouting and insecticide treatment. Research from numerous trials in the upper Midwest, including North Dakota, indicates there is no yield loss at 250 aphids per plant. With higher commodity values, the threshold remains the same.  However, response interval time will decrease to only 5 days. It is important to remember that there still is no yield loss at this threshold. Spraying early (below 250 aphids per plants or tank-mixing insecticide with glyphosate applications) is not recommended in North Dakota. Early insecticide or below threshold treatments simply remove any natural enemies in the field, resulting in a field that is open to re-infestation by immigrating aphids. This could lead to the necessity of re-spraying later in the season.

POTATO LEAFHOPPERS HAVE ARRIVED

Low populations of potato leafhopper have been observed in alfalfa, dry beans, soybeans, and potatoes in eastern North Dakota. This year, migrating potato leafhopper invaded North Dakota in late June from southern states where they overwinter. The adults, which are quite mobile and move from field to field, may migrate from freshly cut alfalfa fields.

The small (1/8 inch), pale green, wedge-shaped adults move rapidly by jumping. Nymphs are pale green, lack wings and exhibit a characteristic sideways walk when disturbed. Nymphs can be found on the undersides of leaves. Nymphs are generally more damaging than adults, since they feed for several weeks on the leaves where they hatched. Sweep nets are useful for confirming potato leafhopper presence in a field. Fields should be scouted to determine whether economic populations are present.  Follow these economic thresholds to help make insecticide spray decisions:

Dry bean = 1 leafhopper per trifoliate leaf
Alfalfa = 1-2 leafhoppers per sweep when alfalfa is 8-14 inches high
Soybean = 5 leafhoppers per plant in vegetative stage and 9 leafhoppers per plant in early bloom stages
Potato = 10-20 adults per 20 sweeps, or 1 nymph per 10 leaves

PRE-HARVEST GLYPHOSATE APPLICATION ON SMALL GRAINS:

Glyphosate is labeled in the use of dry down of the crop in addition to controlling weeds and weed dry down.  Glyphosate takes 7-10 days to effectively kill the growing parts of the plant; the effects are not immediately seen.  If large amounts of green plants are present, swathing will dry them down faster.  However a standing field with a glyphosate application will dry faster than a swathed crop after a rain.  Here are some guidelines to observe when using pre-harvest glyphosate:

1.       Apply glyphosate only after the crop has reached physiological maturity. For most varieties this occurs at a grain moisture content of about 30%.  At this moisture content the grain is in the hard dough stage; if you run your thumb nail across the kernel, the indentation will remain.  Applying glyphosate before physiological maturity can reduce yield, test weight and seed germination.

2.       Because germination can be affected when applied too early, glyphosate should not be used in fields that will be used for seed or on barley intended for malt.

3.       Pre-harvest applications of glyphosate must be made at least 7 days before harvest.

As with all agricultural chemicals, read and follow the label when using herbicides pre-harvest in small grains.

DOWNY MILDEW FOUND IN SUNFLOWERS:

Recently downy mildew has been reported in North Dakota.  At this point in the growing season control is not an option.  It is important to take note of this observation for future planning.  Downy mildew generally causes a systemic infection which results in severely stunted plants and death in the seedling stage.  When systemically infected, leaves may appear �crinkly� with a yellowing on the top sides of the leaf (particularly along the leaf veins) with a white cottony growth on the underside.  Plants will be stunted and growth distorted.  A secondary infection may occur later but usually causes limited damage to the plant.  This infection appears as small chlorotic (yellowed) spots on the leaves and do not result in a systemic infection or stunting.  Because systemically infected plants usually die, yield losses are low due to adjacent sunflowers ability to compensate.  Yield losses are generally not observed if less than 5% of the plants are infected.  Greater loss occurs when infected plants are in rows or clusters, thus reducing the compensatory ability of the sunflower.  Yield loss at that point could be significant.  Secondary infections usually cause no yield losses.  It is important to keep records of downy mildew observation in fields because of the pathogens ability to survive for many years in the soil.  When conditions are favorable, it can germinate and infect plants up to 5 years after the first observation.  Prevention is the best management strategy.  Crop rotations, downy mildew resistant varieties, and seed treatments are recommended when returning to a field with a history of downy mildew.

LATE SEASON WEED ESCAPES IN CORN:

This season many fields are likely to have greater problems with late-emerging weeds than normal.  There are two primary reasons for this:  1) dry and cold conditions in May will suppress activation of soil-applied and excess rain in June will reduce the length of control provided by residual herbicides, and 2) poor canopy development due to cool temperatures, saturated soils and reduced stands will provide a favorable environment for weed growth.  Late emerging weeds are at a competitive disadvantage due to the crops head start.  These weeds may survive and produce seed but yield impact should be minimal unless they are thick enough to create a sod.  Biomass and seed production of weeds emerging at mid-season can be suppressed more than 90% compared to weeds emerging with the crop.  Spraying late season crops may cause more damage to the crop than would be gained by eliminating late emerging weeds.  Most importantly, the majority of herbicide labels prohibit application to larger crops due to problems with crop tolerance or efficacy.  Glyphosate has restrictions in Roundup Ready crops also.  It is important to take into account the increased weed population due to late emerging weeds when developing a weed management plan for 2009.

MORE TEBUCONAZOLES:

The federal registration of Folicur (tebuconazole) in May opened the door for other federal registrations as well, because the patent on Bayer Crop Science�s tebuconazole had expired.  As of July 3, 2008 there are seven tebuconazoles on the North Dakota registration database:

http://www.kellysolution.com/nd/pesticideindext.htm

Folicur 3.6 (Bayer) EPA Reg. No. 264-752
Orius 3.6 F (MANA) EPA Reg. No. 264-752-66222
Monsoon (Loveland Products) EPA Reg. No. 34704-900
Emboss (Winfield Solutions) EPA Reg. No. 1381-203
Embrace (Winfield Solutions/Agriliance) EPA Reg. No. 1381-203
Tegrol 3.6F (Luxembourg-Pamol) EPA Reg. No. 42519-28
TebuStar 3.6L (Albaugh, Inc.) EPA Reg. No. 42750-99

The use pattern of all products is the same, but an applicator MUST have the supplemental label of the appropriate product in hand when the application is made.

County Commissioners, North Dakota State University and U.S. Department of Agriculture cooperating. Duane Hauck, Director, Fargo, North Dakota. Distributed in furtherance of the acts of Congress of May 8 and June 30, 1914. We offer our programs and facilities to all persons regardless of race, color, national origin, religion, gender, disability, age, veterans status, or sexual orientation; and are an equal opportunity employer.
 

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