Slugs Causing Concern Earlier Than Normal
We received numerous reports last week on slugs causing significant feeding injury requiring treatment with molluscicide baits in Ohio. These reports are 2-4 weeks early compared with previous years, and is a result of the warmer winter and March. Slugs hatched out earlier than normal and have reached a size that can cause noticeable feeding injury much sooner. We had addressed this possibility in C.O.R.N. Issue 8, April 10.
In terms of crops, corn and soybeans present two different concerns. With corn’s growing point being below the soil for a few weeks, most of the feeding above ground will be to expanding leaves, and not on the growing tip that would kill the plant. Because of continued growth of corn that will occur, there is some leeway in terms of the time required to make bait application if needed. But keep in mind that the corn is still relatively much smaller than when feeding normally would be occurring, which presents a much more serious situation.
However, the growing point of soybeans is between the cotyledons as the plant emerges from the soil. Thus, the slug is easily able to reach and feed on both the cotyledons and the growing point, making it much easier for slugs to kill the soybean plant as it emerges from the soil. This fact makes immediate treatment of soybeans perhaps more critical if no leaves have yet emerged and expanded.
For growers who have experienced slug issues in the past, it is critical that fields be scouted NOW. If plants have emerged and have leaves, look for the telltale signs of slug feeding. But for crops not yet or just now emerging, or yet to be planted, care should be taken to determine if slugs are present and lying in wait. This is especially critical with soybeans, which could require a bait application just prior to emergence. Use your own past experiences with soybean stand reductions caused by slugs to determine whether an early treatment should be made this year. The two available baits are those containing metaldehyde (Deadline MPs and others), and those with iron phosphate (Sluggo). See our slug fact sheet for more information: http://ohioline.osu.edu/ent-fact/pdf/0020.pdf.
Evaluate Alfalfa Stands
Should I keep this alfalfa stand or rotate it to a different crop? This question comes up at this time of the year because often the farmer plans to harvest a first cutting and then, if the stand is questionable, there is still time to plant corn for silage. There are two basic methods that can be used to evaluate stand productivity. Evaluate the stand density in terms of plants per square foot or evaluate by counting the number of stems per square foot.
Older stands naturally have fewer plants per square foot, but older plants, if they are healthy, produce more stems as compared to a younger plant. Determine the number of plants per square foot immediately after a harvest or any time before a harvest. To evaluate a stand based on stems per square foot, the recommendation is to wait until there is at least 6 inches of growth. Regardless of the method used, sample at least 4-6 random areas within the field to arrive at a decision. Both of these methods assume that the objective is a pure or nearly pure stand of alfalfa.
Alfalfa stands that are over 3 years old should have a minimum of 6 plants per square foot to remain in production. In addition, it is a good idea to actually dig up the plants in some of the sampled areas and split the roots lengthwise to evaluate the health of the plants. In healthy stands, fewer than 30% of plants will show significant discoloration and rot in the crown and taproot. Healthy plants will have vigorous crown shoots distributed evenly around the crown. If over 50% of the plants show signs of root and crown rot, the stand should be rotated to another crop.
The guidelines for alfalfa stand evaluation based on counting the stems per square foot are: 1) greater than 54 stems: no yield reduction 2) 40 to 54 stems: keep the stand but expect some yield reduction and 3) less than 40 stems: consider replacing the stand because yield reduction is significant.
As noted earlier in this article, alfalfa is typically rotated into corn. Occasionally the question comes up regarding whether it is possible to plant alfalfa back into these old alfalfa stands to either thicken up the old stand or to start over with a new seeding. This is not a recommended agronomic practice due to autotoxicity potential. Autotoxicity of alfalfa is defined as an allelopathic effect that inhibits the germination of new alfalfa seedings and/or inhibits the root growth of new seedlings. The general recommendation is to rotate out of alfalfa for one growing season.
The 2012 growing season is providing an opportunity to evaluate marginal alfalfa stands now following a harvest. If the stand doesn’t meet good production criteria, planting it to an annual crop like corn is still an option.
Misc. Emergence Problems in Corn
Corn planting is nearing completion in Ohio. Across the state and within localized areas, corn is at a range of growth stages. Some of the corn planted in April is showing up to 4 leaf collars but in later planted fields, corn is still emerging.
Troubleshooting emergence problems early is critical in identifying solutions and developing successful replant plans, if needed. Here's a list of a few common things to look for if you encounter an emergence problem in corn this spring.(some of this information has been adapted from a newsletter article written by Dr. Greg Roth, my counterpart at Penn State several years ago).
-No seed present. May be due to planter malfunction or bird or rodent damage. The latter often will leave some evidence such as digging or seed or plant parts on the ground.
-Coleoptile (shoot) unfurled, leafing-out underground. Could be due to premature exposure to light in cloddy soil, planting too deep, compaction or soil crusting, extended exposure to acetanilide herbicides under cool wet conditions, combinations of several of these factors, or may be due to extended cool wet conditions alone.
-Seed with poorly developed radicle (root) or coleoptile. Coleoptile tip brown or yellow. Could be seed rots or seed with low vigor. Although corn has just started to emerge or has not yet emerged, growers should carefully inspect seedlings for symptoms of disease, especially in lower lying areas of fields where ponding and saturated soils were more likely. Seeds and seedlings that are brown in color, are soft and fall apart easily while digging are obviously dead or dying. Seeds and seedling roots or shoots that have a weft of white to pinkish mold growing on them are likely victims of fungal attack and will likely die. Pythium and Fusarium are common fungi that attack plants and cause these damping-off or seedling blight symptoms under wet, cool conditions. It is more difficult to diagnose disease damage on plants that also show abnormal growth caused by cold soil conditions or by crusting of the soil surface. However, dark, discolored roots and crowns, instead of a healthy creamish-white appearance, are typical symptoms of seedling diseases problems. So, it is best to check these seedlings very closely for dark brown or soft areas on seedling roots and shoots. Any discoloration will indicate a problem that could worsen if the soils remain cold or wet.
- Seed has swelled but not sprouted. Often poor seed-to-soil contact or shallow planting- seed swelled then dried out. Check seed furrow closure in no-till. Seed may also not be viable.
-Skips associated with discolored and malformed seedlings. May be herbicide damage. Note depth of planting and herbicides applied compared with injury
symptoms such as twisted roots, club roots, or purple plants.
-Seeds hollowed out. Seed corn maggot or wireworm. Look for evidence of the pest to confirm.
-Uneven emergence. May be due to soil moisture and temperature variability within the seed zone. Poor seed to soil contact caused by cloddy soils. Soil crusting. Other conditions that result in uneven emergence already noted above, including feeding by various grub species.
Note patterns of poor emergence. At times they are associated with a particular row, spray width, hybrid, field or residue that may provide some additional clues to the cause. Often two or more stress factors interact to reduce emergence where the crop would have emerged well with just one present. Also, note the population and the variability of the seed spacing. This information will be valuable in the future.
Don’t forget that corn may take up to 3 to 4 weeks to emerge when soil conditions are not favorable (e.g. temperatures below 55 degrees F, inadequate soil moisture). This was widely observed in many fields in 2005 when corn planted in mid April did not emerge until the first or second week of May. As long as stands are not seriously reduced, delayed emergence usually does not have a major negative impact on yield. However, when delayed emergence is associated with uneven plant development, yield potential can be reduced.
- Debbie Brown (Shelby),
- Bruce Clevenger (Defiance),
- Nathan Douridas (FSR Farm Manager),
- David Dugan (Adams, Brown, Highland),
- Mike Gastier (Huron),
- Mark Koenig (Sandusky),
- Ed Lentz (Hancock),
- Amanda Douridas (Champaign),
- Les Ober (Geauga),
- Steve Prochaska (Agronomy Field Specialist),
- Alan Sundermeier (Wood),
- Harold Watters, CPAg/CCA (Agronomy Field Specialist)