April's Ag Advice by April Borders Recently we have experienced freezing temperatures and now we have to be concerned with how our crops faired. The extent of damage to our crops will depend on whether the fields experienced a killing freeze or a frost. Killing "freeze" temperatures for corn and soybeans are at or below 28 degrees F. Temperatures warmer than 28 degrees F would be considered a frost. Duration of the frost or freeze temperatures will also make a difference in the amount of damage seen.
The general recommendation is that we need 72 hours of warmer temperatures after a lethal frost of 28 degrees F or below to evaluate damage to our crops. Since our temperatures have been on the cooler side, it might take more than 72 hours for symptoms to be seen. It generally takes about 72 hours for the plant's systems to begin functioning again so that we can evaluate how seriously the crop has been damaged.
The good news is that most of the corn hasn't reached the V6 stage, which means that the growing point is still below the soil and somewhat protected. The only exception to this is when the temperatures get below 28 degrees F, then the plant may receive damage even below the ground line. Most of the damage you might see on the corn will be minor damage at the tops but it should not hinder regrowth.
If you were one of those early birds that got your soybeans in, you might be in trouble. Soybeans are more vulnerable because the growing point is exposed once the plant has emerged. If you see damage, check your plants carefully to see if the auxiliary buds were damaged. If the auxiliary buds are okay, the plant should resume growth.
Alfalfa may have also been injured. Temperatures in the mid-20s may destroy the growing point on alfalfa causing the plant to be stunted. If there is severe frost damage to the top of the plant the foliage will bend over and the growth of the tips will cease. A good rule of thumb is that if one-third or more of the top growth has been wilted by frost and is drying up, immediate mowing will permit faster development to allow crop regrowth. Harvest of frosted stands that were clipped should be delayed to about the mid-bloom growth stage for the second harvest to allow recovery of stored food reserves. If the damage is less the plant should recover adequately to allow harvest at the normal time.
While established stands of alfalfa can experience temperatures of 28 to 30 degrees and may only wilt for a short period of time, it is a different story for new plantings. New stands of alfalfa may suffer more damage especially if the alfalfa has reached the second trifoliate leaf stage. If temperatures reach 26 degrees F for four hours or more, the new stand may be severely damaged or even killed. If that is the case, consider re-seeding as soon as possible. Keep the good areas and drill into thin or damaged areas.
What about wheat? Wheat is most sensitive to freeze injury at the heading and flowering stage, when two hours of temperatures of 30 degrees F or lower can cause extensive damage. If wheat is at the tillering or jointing stages, temperatures have to drop to 12 to 14 degrees, respectively, before significant injury occurs. Injury symptoms will vary depending on the stage of growth.
The only way to assess the severity of frost or freeze injury to your crops is to wait three to five days and then scout your fields. Remember that cool temperatures following a frost may slow the plants' recovery. For more information about diagnosing frost damage contact the Extension Office.
Well, if we didn't have enough to worry about we also need to be out in the fields scouting for insects. For corn, we should be scouting for cutworms, especially the black cutworms. Check your fields for leaf-feeding, cut, wilting and missing plants.
The alfalfa weevil is starting to make its presence known in the fields. Watch for weevil larva and leaf tips to be skeletonized. Leafhoppers can also be a problem in newly seeded alfalfa. So you need to be out scouting your fields.
If you have questions on frost damage or on insect control for your crops, please give the Extension Office a call at 677-7111.