NDSU Extension - Cavalier County

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7/24/2014

July Update!  Last week’s Ag Alert update was your Langdon Research Extension Center Annual Field Day and Canola Day!

Crop Disease Update:  Dry conditions prior to the rain event on Monday, shifted most all of the disease forecast  risk models down to low risk as most the area had less than an inch through July 20th.  Now we’re back to moderate risk for both sclerotinia and scab.   Though some diseases tend to back off with warmer weather late in the season and crops just starting to flower at this time of the year need a good frost free August and first half of September to achieve good yields to pay for the fungicide.  As of this writing very little sclerotinia in canola and scab in wheat is being reported which will likely change as we move through the next week or two, though the forecast is for decent weather that should limit the amount of new infections.

Weeds! Crops overall still look very good but it is quite disappointing to see the heavy wild oat populations in some small grain fields!   Nice fields can turn ugly in a hurry!  Scout fields now and at harvest to determine the effectiveness of this season's weed control practices. If weeds are present now, determine why they are present. If weeds are present due to herbicide resistance, then weed control and cropping practices must be different next season and beyond.

If a single weed species like wild oats is left behind after a herbicide application and all other susceptible species are controlled, then herbicide-resistant biotypes may be present. If low-level herbicide resistance is present in a field then normal-appearing plants will be next to dead plants and a continuum of responses between normal and dead will likely be present.  If weed resistance is confirmed make sure the heavy patches are cut to stop seed production, hayed if not seeded out or killed with a desiccant or roundup and left to burn after harvest to kill any viable seeds.

The best way to remove weeds at this time of the season is to remove them by hand. Most weeds are producing viable seeds at this time of the season therefore removal of the pulled plants from the field is necessary to prevent distribution of the seeds to the seedbank. Hand-removal or rogueing of resistant biotypes is important to maintaining herbicide effectiveness.

Scouting fields for weeds throughout the growing season is extremely important to maintaining herbicide effectiveness and planning for future weed control decisions.

Drift Assessment! When strange patterns of damage in canola fields line up perfectly with the sprayer boom width or follow typical drift patterns, explanations can be simple: The wrong product was added to the tank, or the right product was applied but on the wrong field.  But situations are often much more complicated — and made even more so by the wide variety of products that go through sprayer tanks. Mixing order becomes a potential problem, with unforeseen consequences if new never-used-before mixes are tried or if the proper mixing order is messed up or if products are not given time to come into suspension before the next product goes in.

Low water volumes can add to the risk. So can water quality, and weather conditions during spraying, and crop staging. So can tank, boom and nozzle cleanout from the previous job. It can also be a combination of many factors, which make disentangling the root cause or causes even more difficult.

The key is to consider all possible variables when working through a spray damage assessment. If you see damage you’ve never experienced before, did you add a new product to the mix this year? Did you follow mixing instructions? Did you use correct water volumes? Did you use a new water source? Were field stage and weather conditions right for all products in the mix?

When injury is scattered throughout the field with patches that appear along with normal emerging plants, areas of low organic matter, headlands, corners or overspray may have more injury, this could be associated with a herbicide carryover (residue) from previous years!

A severe carryover issue can have considerable field variation in acreage affected and severity of plant injury. Uneven plant stands can affect crop maturity and weed pressure.

Canola injury from foliar-applied herbicides may be caused by drift from adjacent fields or from spray tank contamination.   Drift injury generally occurs at field edges or at shelterbelts. However, highly volatile herbicides such as 2,4-D ester, may drift further into the field. In young plants (1– 4 leaf stage), drift injury is easily distinguished from residue injury, since drift causes injury on a larger leaf area. In older plants, drift injury cannot be visually distinguished from residue injury.

Residue in the tank, sumps or filters may affect a larger area compared to residue in the booms or spray jets. Boom and spray jet contamination may dissipate after a few passes with the sprayer, and injury patterns should match the application.

Late Season Assessment: Post flowering, pod fill, pod color change, pre-harvest  (swathing) is a good time to scout for disease severity. Fields with lots of diseased plants may also be poorer candidates for straight cutting due to the increased shattering risk.  Canola diseases that we need to make notes on would include:

Sclerotinia
—Look for areas in the field with lodged or prematurely ripened and bleached areas on plant stems.

Blackleg
—Look for areas in the field with lodged or prematurely ripened plants.  Than examine the basal (bottom) to middle of the stem. When blackleg is severe enough to cause yield loss, the plant will have irregular, knotty, woody cankers at the base of the stem.                                                                                                                                                                

Clubroot
—Above-ground symptoms, including wilting and pre-mature ripening, should be evident in severely-infected plants. Even if you don’t see above ground symptoms, pull plants and look for galls.

Foot rot and brown girdling root rot
—Canola plants pinched off at ground level likely have rhizoctonia foot rot.

For additional help in identifying disease contact my office or our NDSU website: www.ag.ndsu.edu/extension

SOYBEAN ROOT NODULES:  With the right kind of Rhizobia bacteria, nodules may form on the soybean roots. With this symbiotic relationship between the bacteria and the soybean plant, nitrogen gas is fixed into a plant-available nitrogen form. Without the proper bacteria, the plant will not have nodules and the soybean plant will depend on soil-available nitrogen for its growth and development. Without the nodulation, the soybean plant may not be dark green and the yield may be lower than expected. Fields without a soybean history are the most likely fields to show the light green soybean plants. Even if the seed was inoculated with the right bacteria it does not guarantee that nodules will develop. If adverse conditions occurred between the time of inoculation and planting (for instance long storage of the inoculated seed under warm conditions) the bacteria may not have been viable. There can also be field conditions after seeding which inhibit nodulation, for instance saturated soils or very dry soils conditions. It is possible to have nodulation in certain parts of the field and not in the stressed areas. Dig up some plants which appear light green, with a spade (pulling them out may dislodge nodules) and wash the roots in a bucket of water. Observe if the plant has root nodules. Cut a few nodules open and look at the color. Pinkish inside color of the nodules indicates healthy nodules. If no root nodules are found in an area of the field make sure fresh soybean inoculant is used whenever soybeans are planted again in the same field.

Soybean aphids!  The soybean aphids have arrived right on time in southern ND! The IPM Crop Scouts have surveyed over 82 soybean fields last week and soybean aphids were observed in Stutsman, Sargent and Cass Counties of North Dakota. Soybean aphids were low ≈10% incidence and <25 aphids per plant on average. Other neighboring states also have reported non-economic populations of soybean aphids.

Begin scouting soybean fields to determine if soybean aphids are present in fields. See the NDSU YouTube Video on Scouting for Soybean Aphids. No treatment is recommended until aphid densities reach the economic threshold level of 250 aphids per plant and when populations are actively increasing in 80% of field. Early treatments are discouraged so insecticides do not reduce the presence of beneficial predators and parasites.

SUNFLOWER MOTHS:  The sunflower moth migrates to North Dakota from southern states each year. The adult moth is gray, and about 0.4 inch long and 0.75 inch wingspan. Females deposit eggs on the face of the flower during bloom. Damage is caused by the larvae tunneling through the seeds of sunflower heads in late July - August. Scout for the adult moth in the early morning or evening when they are active.

It’s also TIME TO SCOUT FOR BANDED SUNFLOWER MOTH IPM scouts are detecting increasing numbers of banded sunflower moths in pheromone traps. Sunflower should be scouted for banded sunflower moth eggs or adult moths when most of the plants in the field are at plant stage R3 (distinct bud elongated ¾ inch above the nearest leaf, yellow ray petals not visible).

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