Alfalfa suffering--again

Kansas

As if the freeze damage Easter weekend wasn't enough, now recovering stands have taken another hit. Moderate to severe damage to alfalfa stands from common leaf spot and spring/summer black stem have been confirmed in a good percentage of stands across northeast Kansas.

These diseases can be a severe problem in alfalfa, but not generally to the extent we've seen this year. The combined effect of severe freeze damage, heavy rains resulting in waterlogged soils, and some pretty heavy disease pressure have all come together to beat stands back again. Brand new stands have, in some cases, been killed outright. Other stand damage has depended on severity of the freeze, regrowth before the rains, and rainfall. Some stands have literally melted away, while others are holding on with yellowing leaves.

Unfortunately, there is little we can do at this point other than wait for recovery. Stands that may have been struggling before are really showing damage now. Others still have a sound growing point that should try and regrow with the return of some drier and sunny weather. Fungicides will likely do little good and most aren't labeled for alfalfa.

Insecticides may be warranted if weevil and/or aphid pressure is severe. In many stands, beneficial lady beetle larvae have also been present which is keeping aphid damage low.

What can you expect? Plants damaged beyond singed leaf margins can be expected to become harvest ready later than normal. These plants may not bloom like normal. Don't rely strictly on bloom for harvest decisions. Use calendar dates or appearance of new crown shoots instead. If growing points appear healthy, continue to monitor. Avoid shredding or grazing this time around--the plants are already stressed enough. Remember: plants 6 inches or shorter were pulling from root reserves already depleted by early growth then freeze regrowth--making their recovery slower. Some new seedings are having a very difficult time of responding to yet another taxing on already low root reserves.

It may also be time to evaluate feed availability: Depending on how alfalfa stands recover and brome responds from now until harvest will make a big difference in what we have available the rest of the year. Continue to monitor alfalfa stands closely: 2007 could be an opportunity to look closely at stands to determine if sufficient plants are available for economic production. We do have some guidelines that may assist in your evaluation as stands come back. Make sure fertility needs are being met. If fertilizer has been 'shorted' to a stand, it may be time to correct deficiencies to maintain the stand. Phosphorous is of particular importance.

Bagworms

This is typically the time of year when we start hearing questions about bagworms. However, the second week of June is about the halfway point of the 4 to 5 week period of bagworm egg hatch. This is the earliest bagworms are still small and go undetected because they are not causing noticeable damage. Even if the small bagworms are observed, insecticide treatments are not recommended during this time in the egg hatch period unless you are committed to applying two treatments. A single application now or even in to early June can give a false sense of security that you have bagworms under control when, in fact, many have yet to hatch. When considering a single spray treatment, the last week of June or the first week of July is the best time to treat for current-season bagworms. At that time, all eggs will have hatched.

For more information on products and timing, contact your District Extension Office for information.

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6/4/07

Date: 5/25/07

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