Crop & Pest Report - All
Fields need to be scouted by sampling at least 5 sites while walking a W-pattern and inspecting about 10 plants per site. Avoid sampling the edges of field.
POTATO LEAFHOPPERS: Potato leafhopper was one of the many migratory insect pests that invaded North Dakota this year. Adults are quite mobile and move from field to field, and may migrate from freshly cut alfalfa fields. Other crops attacked include potato, dry bean and soybean. The small (⅛ 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.
Damage by leafhoppers is referred to as hopper-burn. Foliage becomes dwarfed, crinkled and curled. Small triangular brown areas appear at the tips of leaves, gradually spreading around the entire leaf margin. 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 need to be scouted to determine whether economic populations are present. Examine the underside of leaves for adult and nymph leafhoppers. Follow these economic thresholds to help make insecticide spray decisions for potato leafhoppers:
Dry bean = 1 leafhopper (either adult or nymph) 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
Potato = 10-20 adults per 20 sweeps, or 1 nymph per 10 leaves
SPIDER MITES: It is not surprising to see spider mites showing up with the hot dry weather. Mites are small and magnification is required to see them. A quick sampling procedure to determine whether mites are present is to hold a piece of white paper below leaves, then beat them to dislodge the mites. The mites appear as tiny dust specks; however, they will move after being knocked off the leaf. Another method is to pull plants and examine the undersides of the leaves for mites and webbing. Begin from the bottom of plants and move upwards into the canopy. Feeding damage by mites first appears as small yellow spots (stippling). As feeding activity increases, leaves become yellow, bronzed or brown, and eventually shed from the plant. Be sure to scout during full pod (R4) through beginning seed (R5) stages since these crop stages are the most important contributors to soybean yield. Mite infestations typically are first noted near field edges.
Spider Mite Threshold: There is no specific threshold that has been developed for two-spotted spider mite in dry beans or soybeans. Treatment is advised when heavy stippling on lower leaves with some stippling progressing into middle canopy. Mites may be present in middle canopy with scattered colonies in upper canopy. Leaf yellowing is common on lower leaves.
Pest Management: If spider mites are a problem along with leafhoppers, the only pyrethroid that will work is bifenthrin (Tundra, Sniper, Brigade, Fanfare, Bifenture, etc.) in dry beans and soybeans. While other pyrethroids, such as lambda-cyhalothrin (Warrior, Silencer, etc.) will control leafhoppers, they will cause spider mites to flare up and then you may well have to spray again with bifenthrin or an organophosphate (OP) insecticide.
Two active ingredients of OP insecticides for control of leafhoppers and spider mites are chlorpyrifos and dimethoate. However, chlorpyrifos (Lorsban and generics) is NOT registered for foliar application in dry bean. It is only registered as a preplant broadcast or at-plant T-band for control of seed corn maggot in dry beans. However, chlorpyrifos is labeled for both leafhoppers and spider mites in soybeans. Dimethoate will control both leafhoppers and spider mites in dry beans and soybeans, but has a shorter residual than bifenthrin. We think it’s realistic to expect about a 7 to 10 day residual from bifenthrin (if it is hot, residual may be decreased), a 4 to 7 day residual from chlorpyrifos, and a 3 to 5 day residual from dimethoate. It is extremely important to scout and monitor for recurring leafhopper and especially spider mite populations after spraying. Check your fields five days after treatment and again at regular intervals to make sure your control is holding. If newly hatched spider mites are observed after 5 days, a second treatment may be necessary with a different insecticide mode of action. For example, if you use bifenthrin (pyrethroid) for the first application, use a non-pyrethroid product, such as dimethoate or chlorpyrifos (OP), for the 2nd application.
DRY BEANS AND SOYBEANS:
Bifenthrin 2EC product rates:
Leafhoppers = 1.6 to 6.4 fl oz per acre, 14 day PHI
Spider mites = 5.12 to 6.4 fl oz per acre, 14 day PHI
*If you use bifenthrin, use the high rate for spider mite control.
Dimethoate 4E products
Leafhoppers and Spider mites = 0.5 to 1 pint per acre, no PHI (do not feed to livestock)
Bifenthrin 2EC products
Leafhoppers = 1 to 2 pts per acre, 28 day PHI
Spider mites = 0.5 to 1 pt per acre, 28 day PHI
Janet J. Knodel, Extension Entomologist
Patrick Beauzay, Research Specialist
SPIDER MITES: Corn is susceptible to spider mite damage from tasseling through the hard dough stage. When corn has reached the hard dough stage, it is no longer susceptible. The economic injury level (EIL, Table 1) is based on the market value, % infested leaves per plant, % of total leaf area damaged and control cost per acre (Source: Texas A&M University, Extension Publication E-400)
To calculate EIL for corn market values that exceed $700 per acre, use the following formulas from Dr. R. Wright of University of Nebraska (Source: http://elkhorn.unl.edu/epublic/live/g1167/build/#target7):
- For percent infested leaves = (cost of control x 600) ÷ (price per bushel x bushel yield)
- For percent of leaf area damage = (cost of control x 312) ÷ (price per bushel x bushel yield)
CORN LEAF APHID: Corn is susceptible to aphid injury from late whorl through pollination. Corn leaf aphids are bluish grey, pear-shaped, soft-bodies insects with dark short cornicles (two projections at rear end of body). Symptoms of heavily infested corn by aphids include wilted, curled or yellowed leaves, and even stunted plants and shriveled ears. During pollen shed, large populations of aphids on silks can interfere with pollination due to aphid’s honeydew excretions and black sooty mold fungus that grows on honeydew. The action threshold is when 50% of the plants are infested with colonies of over 75 aphids per plant, and plants are drought stressed. Lady beetles, green lacewings, syrphid fly larvae and parasitic wasps play a major role in reducing aphid populations. When natural enemies are present in large numbers, and the crop is well developed, farmers are discouraged from spraying fields.
Janet J. Knodel
Mature fields are not surveyed, because of the difficulty of distinguishing diseases when crops are ripe. As the crops develop grain and become more mature, more diseases become evident, although a few are occurring late enough to cause limited yield or test weight loss.
For diseases caused by fungi, tan spot was the most common leaf spot disease, still detectable in 80% of fields surveyed, with an average severity on the flag leaf of 5%. Stripe rust was the second most common disease observed, in 23% of surveyed fields. Field scouts did not report any observations of common wheat leaf rust. Septoria (Stagnospora) leaf spot also was evident, in 20% of surveyed fields, and half of these also showed glume blotch, the head infection phase of this fungus. Fusarium head blight (scab) symptoms were observed in 12% of surveyed fields, with most of these found in northern counties, but field severity was very low, averaging 1.7%. Loose smut was in 18% of surveyed fields, and within these fields, 11% of heads were smutted. These fields high in loose smut should have had a systemic seed treatment applied, as these levels are well above the 2% level that makes seed treatment economical.
For bacterial and viral diseases, bacterial leaf streak was observed in 14% of surveyed fields and more than half of these fields also exhibited black chaff symptoms on the grain heads. The level of bacterial leaf streak is much lower than in 2011. Barley yellow dwarf virus symptoms were observed in 12% of surveyed fields and wheat streak mosaic in 7%. The golden yellow discoloration of flag leaves associated with barley yellow dwarf symptoms has become more evident in the past week.
Extension Plant Pathologist, Cereals
F. Adnan Akyuz, Ph.D.
Assistant Professor of Climatology
North Dakota State Climatologist
July 10: Hettinger Research Extension Center – Hettinger, ND.
July 11: Dickinson Research Extension Center – Dickinson, ND.
July 12: Pulse Tour: North Central Research Ext. Center – Minot, ND.
July 13: Pulse Tour: Carrington Res. Extension Center, Carrington, ND.
July 16: Agronomy Seed Farm – Casselton, ND.
July 17: Carrington Research Extension Center – Carrington, ND.
July 18: North Central Research Extension Center – Minot, ND.
July 19: Canola Tour & Field Day: Langdon REC – Langdon, ND.
July 24: Williston Research Extension Center – Williston, ND.
July 25: Nesson Valley Irrigation Tour – Williston, ND.
July 31: Oakes Irrigation Research Site – Oakes, ND.
However, little to no feeding injury has been observed yet on wheat heads or flag leaves. It is important for the growers to scout field edges and within the field to determine if the field needs to be treated for grasshoppers. The action threshold for nymphs (immature grasshopper without wings) is 50-75 per square yard in field margins and 30-45 per square yard within the field. For adult grasshoppers, the action threshold is lower: 21-40 in field margins and 8-14 within the field. Four 180 degree sweeps with a 15-inch sweep net can be used to estimate one square yard.
We feel that the grasshopper situation has the potential to get worse, especially if the weather continues to be hot and dry. Flowering or heading cereal crops are vulnerable to grasshopper feeding injury on kernels and leaves (leaf stripping). As wheat matures and the only green tissue is just below the head, severe head cutting can occur. As wheat fully ripens and matures, grasshoppers will move out of wheat in huge numbers and into other late-season crops, such as corn, sunflower or flax that are still green.
A pyrethroid, such as Baythroid XL, Warrior II, or Mustang Max (or their generic equivalents) is recommended for control of grasshoppers in wheat. HOWEVER, it is important to note that not all of these pyrethroids have the same pre-harvest interval. Of these, Mustang Max has the shortest PHI at 14 days. Always read and understand the label (e.g., application rates, PHI). It is extremely important to observe the PHI when selecting and using any pesticide as we get closer to harvest.
Dimilin 2L (diflubenzuron) has good performance against grasshoppers, but is a growth regulator and only works on 1st, 2nd, and 3rd instar nymphs. In some areas, it may be too late to use this product if large nymphs (>½ inch) and adults are appearing. Dimilin 2L has a long PHI of 50 days, and in North Dakota Dimilin 2L can only be used west of US Highway 281.
Janet J. Knodel
The maggot chews and partially cuts the stem so it pulls out very easily. Historically, infestation levels rarely exceed 2 percent white heads. Recent pest surveys in North Dakota have detected higher levels of wheat stem maggot in wheat. Field scouts recorded higher average infestation levels from 2007 to 2010: 17.0% in 2007, 5.8% in 2008, 4.6% in 2009, and 7.0% in 2010. The principal cultivated crop hosts of the wheat stem maggot are spring wheat, rye and barley, with wheat being preferred. It also attacks bluegrass, timothy, quackgrass, slender and western wheat grass, wild barley, bromegrass, green and yellow foxtail and bluestem grass. Wheat stem maggot can be controlled with an insecticide application applied early in the season from the 4-6 leaf stage through the flag leaf stage, although no action threshold exists.
Janet J. Knodel
Early-planted sunflowers are just starting to bloom and spray decisions need to be made at early bloom for optimal control of head-infesting insect pests.
Banded Sunflower Moth Sampling during Day
Sampling sites should be at least 75 to 100 feet from the field margins. In monitoring a field, use the X pattern, counting moths on 20 plants per sampling site to obtain the total number of moths per 100 plants. Sampling should be conducted in the late bud stage (R3), usually during mid-July. If treatment is warranted, it should be applied at the R5.1 sunflower plant growth stage (when 10% of head area has disk flowers that are flowering or completed flowering). During the day (late morning to early afternoon) the moths remain quiet, resting on upper or lower surfaces of the leaves of sunflower plants. When disturbed, they flutter from plant to plant. When sampling for moths during day, the decision to treat is based on comparing the average number of adult moths in the field to the EIL for moths. The EIL is the number of moths per head that will, if not managed, result in seed damage with a value equal to the cost of treatment. Use the following formula based on treatment costs, plant population and market price to determine the adult moth EIL for day sampling.
Chemical Control and Application Timing for Banded Sunflower Moth
Chemical treatment is directed at the larval stage of the banded sunflower moth which is the actual damaging stage. Once the decision to treat has been made, it is critical to correctly time the spray application to get maximum control. The best sunflower plant stage to treat is the R5.1 growth stage, or when pollen shed is just beginning. This is the time when most moth eggs have hatched and larvae are present, but before the head has seeds forming. At this time the larvae are beginning to feed on the disk flowers, are exposed on the head, and are susceptible to the insecticide treatment. On older plants where the seeds have started maturing, most larvae will be feeding within the seeds or under the protection of the florets and will be protected from the insecticide. By then, much of the feeding damage has already occurred. Application at an earlier growth stage may be warranted if monitoring reveals earlier than normal egg-laying activity. The banded sunflower moth, seed weevil and the lygus bug have all impacted quality of confection sunflowers the past three to four seasons. It is recommended at this time, that sunflowers grown for these markets be treated a minimum of two times, once at early flowering and again 5 to 7 days later. With this type of program, a window of protection should be provided to minimize impact from all three of these seed-damaging insect pests.
Please see the 2012 North Dakota Field Crop Insect Management Guide for insecticides registered in sunflower: http://www.ag.ndsu.edu/pubs/plantsci/pests/e1143w1.htm
Janet J. Knodel
Observational data collected earlier this week from our field trials near Mapleton and Leonard show that natural enemies, such as lady beetles and lacewings, are present and appear to be a factor in keeping aphid numbers low. Last week’s heat also was not conducive for aphid population growth. However, it is important for growers to continue to scout for soybean aphids as the potential for migratory aphids increases in the weeks ahead. Remember, don’t spray unless and until you have to.
Dr. Ian MacRae, entomologist with the University of Minnesota’s NWROC at Crookston, has been receiving calls about spider mites in soybean. The hot dry conditions we have been experiencing across the region are conducive for rapid spider mite population increase. Growers should scout soybean and dry bean for spider mites and/or spider mite damage. Spider mites can be detected by gently beating plants over a sheet of white paper and examining for mites with a hand lens. Light-colored mites with two dark spots on the body are adult spider mites. Webbing made by the mites also can be seen on the leaves. Damage first appears as stippling (yellow spotting) on the lower leaves. As damage progresses, leaves will become browinsh or bronze, and damage will progress upwards through the canopy. Damage in a field may first appear in isolated areas. Damaged areas become more expansive as populations increase and spider mites emigrate to adjacent areas in the field. This pattern typically follows the direction of prevailing winds. Drs. Bruce Potter and Ken Ostlie of the University of Minnesota have prepared a website with excellent information on spider mites, including a treatment threshold: http://www.soybeans.umn.edu/crop/insects/spider_mites.htm
Pyrethroids, with the exception of bifenthrin, will cause spider mite populations to flare up. If control is needed, we recommend using an organophosphate such as chlorpyrifos (e.g. Lorsban) or dimethoate, or a bifenthrin product such as Brigade or Fanfare. Pyrethroid/OP combo products such as Cobalt Advanced can also be used. It is critical to use a sufficient spray volume (at least 20 GPA) to attain good coverage. Fields should be scouted every 4 or 5 days after spraying to make sure spider mites have been controlled. For a list of products registered in soybean and dry bean, please consult the North Dakota Field Insect Management Guide E-1143: http://www.ag.ndsu.edu/pubs/plantsci/pests/e1143w1.htm
Tile drainage does not remove plant available water, and normally ensures good and deep root development. However, we do not just need to look at removing water but we should also consider managed drainage (controlled drainage). We should only let water drain when we really do not need it and keep water back in the event of drier weather conditions. In order to manage the water coming out of the tile one needs to have some form of water management structure at the end of the tile line. Images 1 and 2 show a table-top model of a water management/ control structure. The actual structure extends from the tile depth to above the ground surface (Image 3). Tile on the right comes from the field and the pipe to the left goes to the ditch. In the center of the water management structure there are baffles or panels that can be inserted or removed to raise or lower the water table depth on a portion of the field (Image 2).
The water table uphill from the structure can be managed with these structures. Under dry conditions, with panels inserted up to some depth above the tile (to perhaps within 24 inches of the field surface) it may be possible with proper management and favorable rainfall timing, to store more water in the soil profile than would be the case with a conventional (no management structure) drainage system. However if wet conditions ensue, the producer has the ability to open the structure and subsurface drain the field. A lift or pumping station is another structure that creates an opportunity to manage the water table, depending on the slope of the field. The pump can either be turned on or off, to stop the water from being drained from the field. Last week I passed a lift station (Image 4) that was still pumping water. Knowing that we are in a drier period, I would turn the pump off and monitor the water table in the sump and turn on the pump again when needed.
In order to be most effective, water management structures need to be incorporated in the field plan during the design phase of a drainage project. A structure is typically used to manage the water table over an area of the field with about one foot elevation change, so there may be a need for multiple structures, tiling on the contour, or the incorporation of in-line management structures.
A regional Extension publication addressing frequently asked questions about drainage water management is available at http://www.extension.umn.edu/DrainageOutlet/QandA.html.
Extension Agronomist Broadleaf Crops