Number 2
October 5, 2005
1.Timing of cheatgrass herbicides
2. Use of nitrogen in carrier with cheatgrass herbicides
3. Bindweed control
4.Nitrogen and its effect on wheat yield components in fall
5. Evaluating alfalfa stands
6. Killing off old stands of alfalfa
1. Timing of Cheatgrass Herbicides
Producers who want to treat their fields of continuous wheat with a cheatgrass herbicide have to decide when to apply it. Should they spend the money now or wait until spring to see if the wheat is going to yield enough to pay for it? Each of the most commonly used cheatgrass herbicides – Finesse Grass and Broadleaf, Maverick, Olympus, and Olympus Flex – is most effective on cheatgrass when applied in the fall. They can also be effective when applied in winter if the cheat is actively growing, or in the early spring, but control is most consistent when applied in the fall. These products should be applied when the cheatgrass is small and actively growing, and when the wheat has at least two leaves but prior to jointing.
One benefit of fall application compared to spring application is that a fall application helps minimize rotational restrictions. Finesse Grass and Broadleaf and Maverick have longer rotational restrictions than Olympus or Olympus Flex.
The cheatgrass species present is a very important factor in the level of control to expect. All the listed herbicides can provide very good control of true cheat, but are less effective on downy brome. In fact, Finesse Grass and Broadleaf is quite poor for control of downy brome.
Also, none of these cheat herbicides controls feral rye. To suppress feral rye in wheat, producers would have to use Beyond herbicide and a Clearfield wheat variety. The label of Beyond now calls for a fall application, followed by a spring application for suppression of feral rye.
Producers need to realize that rye and ryegrass are not the same plant. Feral rye and Italian ryegrass are two different grassy weeds. Olympus Flex can give very good ryegrass control, but will not control rye. It is important that producers make that distinction when they hear or read advertisements about ryegrass control with Olympus Flex.
-- Dallas Peterson, Weed Management Specialist
785-532-5776
2. Use of Nitrogen in Carrier with Cheatgrass Herbicides
Producers may want to apply some of their N to wheat by including liquid UAN in the carrier with their cheatgrass herbicides. Nitrogen is labeled for use in the carrier with each of these herbicides, but Monsanto discourages the use of N in the carrier with Maverick. One of the primary concerns with applying these herbicides with UAN carrier is that surfactant still needs to be added to the spray. The addition of surfactant with the N fertilizer can greatly increase leaf burn on the wheat and lower grazing potential. The general guideline for applying these herbicides with fertilizer is to use no more than 50 percent fertilizer blend with water and a maximum of 30 lbs N per acre.
Research at K-State has actually shown an improvement in cheatgrass control when these herbicides are applied with 50 percent fertilizer carrier solution. However, if warm sunny weather follows application, there is often some foliar leaf burn on the wheat. The leaf burn is generally temporary in nature and has not caused a reduction in wheat grain yields in our research. Producers need to be aware of the label restrictions and follow the company guidelines.
-- Dallas Peterson, Weed Management Specialist
785-532-5776
3. Bindweed Control
Late summer and fall can be an excellent time to apply herbicides for field bindweed control. Bindweed seems to be more susceptible to herbicides at this time of year because of improved absorption and translocation to the root system. Bindweed foliage will tolerate light frost. Actually, herbicide treatments seem to be most effective after a light frost, as long as the foliage is not damaged by a hard freeze.
The most effective herbicides for bindweed control include Tordon, Paramount, 2,4-D, dicamba, and glyphosate. The best herbicide choice may depend on the producer’s cropping plans. Tordon plus 2,4-D is one of the best bindweed treatments, but can only be applied to grass or to fallow fields going back to wheat or sorghum. Paramount can provide similar field bindweed control to Tordon treatments, and can be used in noncropland or as a preplant treatment prior to planting wheat in the fall or sorghum in the spring.
Dicamba, 2,4-D, and glyphosate have fewer rotational crop restrictions than Tordon or Paramount. Glyphosate has no recropping restrictions. Dicamba and 2,4-D applications in the fall should have no issues with spring planted crops, but at least one to two weeks should be allowed between application and planting wheat. A waiting interval of at least one week after herbicide application should be allowed before tillage to allow time for herbicide absorption and translocation in the plants. Refer to product labels for recommended rates and recropping guidelines.
-- Dallas Peterson, Weed Management Specialist
785-532-5776
4. Nitrogen and Its Effect on Wheat Yield Components in Fall
Nitrogen deficiency of wheat in the fall is becoming more common as more producers are moving toward no-till and/or more intensive rotations. One reason is that producers are not applying as much preplant N now, in general, compared to traditional conventional or reduced-till management systems. Much of preplant N in conventional or reduced-till systems has traditionally been supplied as anhydrous ammonia, and these applications were necessarily knifed into the soil away from previous crop residues.
Another reason for the increase in early-season N deficiency is that in no-till and/or more intensive rotations less soil organic N may be mineralized in the fall. This reduces the amount of soil N available to wheat in the fall. As a result of these and other factors, fall N nutrition of wheat has become a larger issue than in the past.
Last year, many no-till producers throughout Kansas found their wheat was yellowish in the fall and early winter and in some cases had smaller than expected root systems. There are many factors that can cause yellow wheat, but N deficiency was a cause of much of the yellow wheat last fall. How much will N deficiency in the fall reduce wheat yields? There’s no definitive answer, but we can say that N deficiency in the fall will reduce tillering and root development. Where roots development is inadequate, the uptake of water, as well as phosphorus and other nutrients, may be reduced. If the wheat remains N deficient through jointing the following spring, potential head size may also be reduced.
-- Dale Leikam, Nutrient Management Specialist
785-532-6183
5. Evaluating Alfalfa Stands
Alfalfa stands can be productive for 5 years or more in Kansas, but production usually starts to decline after the first year or two. At some point, a decision has to be made about whether to keep the stand for one more year, or destroy it.Producers who have an alfalfa stand that has been established for 4-5 yearsor more should evaluate their field this fall to see if it’s time to destroy it and either plant another crop or go back to alfalfa.Evaluating a stand in the fall is better than waiting until spring because it gives producers more time to plan out what they want to do with the stand.
Producers should count the number of stems per square foot at several locations in the field. Only stems over 2 inches tall should be counted. Research at the University of Wisconsinhas found that a stem count is a much more accurate method of estimating the yield potential of an alfalfa field than plant count. Plant density is a poor estimator of yield potential because an individual plant may have few shoots and contribute little to yield. A stand of alfalfa should have at least 20-25 stems per square foot to justify keeping it for another year. A stand with 20 stems per square foot will typically have a yield potential of about 2 tons per acre, under optimal management and growing conditions.
When evaluating the stand, producers should also dig up some plants and examine the crowns for size, symmetry, and the number of shoots present. Roots should be cut lengthwise to check for rot or discoloration in the crown and root. Healthy stands have fewer than 30 percent of the plants with significant discoloration or rot.
-- Jim Shroyer
6. Killing Old Stands of Alfalfa
Fall is probably the best time to kill out an old stand of alfalfa. Producers should spray alfalfa when it has about 8-12 inches of regrowth. At that point, the flow of carbohydrates is moving down again, into the root systems, so herbicide uptake will be increased. If the herbicide is applied before that time, carbohydrates are still moving upward from the root reserves into topgrowth.
A light frost in the fall won’t affect alfalfa growth or herbicide uptake significantly, but a hard freeze will. So herbicides should be applied before a hard freeze, when temperatures get down into the mid-20’s. Producers could also wait until after the first cutting in the spring, when there is 8-12 inches of regrowth, to kill out the stand with herbicides. But alfalfa is harder to kill at that time of year.
To kill an alfalfa stand, it’s best to use 1 quart of 2,4-D ester and a half-pint of dicamba. Producers could also use 2 quarts of 2,4-D alone, but that’s generally not as effective as the 2,4-D/dicamba combination. Mixing glyphosate with the 2,4-D or dicamba can also provide good alfalfa control, as well as control any grasses that may also be present in the field.
-- Dallas Peterson, Weed Management Specialist
785-532-5776
These e-Updates are a regular weekly item from K-State Extension Agronomy. All of the Research and Extension faculty in Agronomy will be involved as sources from time to time. If you have any questions or suggestions for topics you'd like to have us address in this weekly update, contact Jim Shroyer, Research and Extension Crop Production Specialist and State Extension Agronomy Leader
785-532-0397