Traill County Ag Alert Newsletter

Traill County Ag Alert Newsletter

July 11, 2008

Issue #10 July 11, 2008

RAINFALL & GROWING DEGREE DAYS (GDD)

Location                                   Mayville           Hillsboro          Galesburg
Corn GDD                               840                   851                   841
Compared to 2007                     -231                  -230                  -221
5 Year Average                        -102                  -94                   -66

Wheat GDD                            1895                 1901                 1908
Compared to 2007                     -347                  -352                  -318
5 Year Average                        -184                  -180                  -121

TIME TO SCOUT FOR SOYBEAN APHIDS
Soybean aphid populations have been low and below economic threshold levels so far. However, aphid populations will continue to increase and soybean fields should be scouted. 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 (source: Ian MacRae, UMN).

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, who are quite mobile and move from field to field, may migrate from freshly cut alfalfa fields.

The small (c inch), pale green, wedge-shaped adults move rapidly by jumping. Nymphs are paler 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

GLYPHOSATE & OTHER HERBICIDES PRE-HARVEST IN SMALL-GRAINS
With winter wheat in the starting to turn and other small grains not that far behind, it is now time to think about harvesting. If green weeds in the crop will hinder the harvesting process there are several herbicides labeled for pre-harvest weed control (refer to the 2008 Weed Control Guide and the labels of approved products for additional details). Weed control with pre-harvest herbicides, however, is generally disappointing as weeds at this time are tall, nearing maturity and slow growing. Furthermore, green weeds can take a week or more to dry down even with an effective treatment.

Glyphosate, in addition to controlling weeds, is labeled for use in aiding the dry down of the crop itself (as opposed to controlling and drying down weeds in the crop). Glyphosate is a systemic herbicide and takes from 7 to 10 days to effectively kill the growing parts of the crop; consequently an increased rate in dry down is not immediately visible. Traditionally, fields that had excessive green material were swathed. Swathing enables faster dry down than pre-harvest glyphosate if significant levels of green material are present in the crop. A standing crop that has been treated with glyphosate, however, will dry faster than a swathed field after a rain.

When using glyphosate pre-harvest observe the following guidelines:
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.

NDSU IPM SCOUTS FIND MORE WHEAT LEAF RUST
Wheat: Detection of leaf rust picked up during the 4th of July week, with 11.3% of the 168 wheat fields scouted showing some level of leaf rust. These detections were all in counties in the southeast quadrant of the state. The average severity of leaf rust in infected winter wheat fields was 9.2%, while average severity in positive spring wheat fields was 1.9%.

Tan spot remained the most common wheat disease observed, in 60% of the fields, with the northeast region showing the least amount of disease. Loose smut was increasingly observed, in 15% of the surveyed fields, and the average percent incidence of tillers with symptoms was 5.8%, but as high as 20% in one field. Loose smut is controlled with systemic seed treatments.

Other wheat diseases observed included Septoria leaf blotch, bacterial leaf blight, black chaff, and some powdery mildew, all generally infrequently, although Septoria levels are increasing now that the crops are headed out.

Barley: The NDSU field scouts looked at 20 barley fields last week. Fungal leaf spots, including net blotch and those caused by Septoria species, were generally the only diseases observed in barley.

PRE-HARVEST INTERVALS FOR SMALL GRAIN FUNGICIDES cont.
Last week’s Ag Alert contained a table indicating the pre-harvest interval required for common small grain foliar fungicides. This table related to pre-harvest intervals for wheat or barley used for grain. Different limitations may apply if the crop is used for forage or silage, grazed or used for bedding. Individual labels must be consulted for these additional restrictions.

Inadvertently, last week’s table on pre-harvest intervals did not include the mancozeb products such as Dithane, Manzate, and Penncozeb, nor were the copper containing products, such as Champ, Cuprofix and Kocide, included. The pre-harvest interval for mancozeb products is 26 days, and the copper product labels say “the first application may be made at early heading, and may be followed with another application 10 days later”.

TAKE NOTE OF DOWNY MILDEW OF SUNFLOWER
Downy mildew of sunflower has recently been observed in North Dakota. Although control of the disease at this point in the season is not possible, the observation of downy mildew is important for future years. Downy mildew generally causes a systemic infection, which results in a severely stunted plant and death in the seedling stage. Although it can also cause a secondary infection, which occurs later and causes limited damage to plants. When plants are systemically-infected with downy mildew they will often be stunted and their growth will be distorted.

The leaves may appear ‘crinkly’ with yellowing on the top sides of the leaves (particularly along the leaf veins) with a white cottony growth on the underside. Secondary infections appear as small chlorotic (yellowed) spots on the leaves and do not result in a systemic infection or stunting.

Yield losses to downy mildew are generally low because systemically infected plants often die, and adjacent sunflowers are able to compensate by producing larger heads. In general, yield loss is not usually observed if less than 5% of the plants are infected. However, when infected plants are in clusters or in rows the compensatory ability of sunflowers is reduced, and yield loss in that part of the field may be significant.

Secondary infection usually causes no yield loss. Once downy mildew occurs there are no tools to control it, thus, prevention of downy mildew is the best management strategy. The pathogen produces spores that may remain in the soil for many years, and when the environment is favorable, may germinate and cause infection for up to five years after downy mildew was first observed in the field. For this reason, it is important to take note of any downy mildew occurring in your fields. Several years of rotation, downy mildew resistant varieties, and seed treatments are recommended when returning to a field with a history of downy mildew.

NDSU Extension Service, North Dakota State University of Agriculture and Applied Science, and U.S. Department of Agriculture cooperating, Duane Hauck, Director, Fargo, North Dakota. Distributed in furtherance of 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, sex, handicap, age, Vietnam era veteran status, or sexual orientation; and are an equal opportunity employer.

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Traill County Extension Office

P.O. Box 730

Hillsboro, ND 58045

701-636-5665 or toll-free1-877-843-6383