April 2007
Planning, Patience Imperative During Planting Season

When faced with seed performance problems in the early season, there is usually little that the affected grower can do. After the seed has been planted and a problem develops, often the only thing the experts can tell you is the color of the train that ran over you.

In other words, seed performance issues are best handled with good planning and by avoiding situations that are likely to lead to problems. Naturally, the purchase of certified seed with all of the special attention and frequent inspections that it has received is an excellent way to reduce risk and achieve your target yields, but locating and buying quality seed is only the beginning. There are a number of other factors that can have a significant influence on early season seed performance.

What are some of these factors? We often hear that seed physiological age has an effect on yield and quality. The down side is that this factor can be very difficult to quantify, let alone control. The influence of physiological age can be readily demonstrated but has proven difficult to predict. Recent research in England and at Washington State University could help to make some sense out of the physiological age conundrum, but more work is needed. In any case, in the vast majority of instances, the physiological age of your seed lot will be well within acceptable parameters.

One of the major problems faced by both seed and commercial potato growers is seed piece decay. Seed decay can lead directly to lost production through the failure to establish a good stand. Even if the stand is adequate, losses in yield and quality can still occur because seed decay may cause weakened plants or eventual stand losses due to diseases such as blackleg. There are actually two types of seed decay: dry rot caused by fusarium and soft rot caused by the bacterium erwinia carotovora. The two types of decay are often found together in the same seed piece. Both types are greatly favored when potato tubers get wounded, which is, of course, what happens when we cut tubers to make seed pieces.

Since wounding is an unavoidable part of seed cutting, one of the best ways to combat seed decay problems is to use a seed-piece treatment. Most seed treatments consist of a dust formulation that also contains a fungicide. These treatments are designed to help dry out the wet, freshly cut surfaces of the seed pieces while also providing protection from dry rot through the action of the fungicide. The new, low-volume liquid seed piece treatments also do an excellent job of managing dry rot. Seed piece treatments are cheap insurance against seed decay and can help you avoid problems.

Seed treatments help to buy time for wound healing” or “suberization” of all the freshly cut surfaces on the newly-created seed pieces. The two types of seed decay have different abilities to breach the new wound barriers. For instance, soft rot is stopped by the suberin barrier after seed has been healed for 48 hours or so, while dry rot is not. The extra protection provided by a mature suberin layer (five to six days of healing, minimum) is needed to stop the dry rot organism. Another problem is that there are no seed treatments that directly control soft rot.

One method to combat the soft rot pathogen is to use whole or “single drop” seed. Another method is to cut and heal seed before planting. This “precutting” process allows the establishment of good, strong suberin barriers before the seed pieces are placed into the hostile environment of the soil. A word of caution: Great care must be taken to provide the right conditions to heal cut seed properly or major difficulties can result one of those “train wrecks” I talked about earlier. For healing seed, there are three requirements: high humidity, temperatures between 50˚ F and 55˚ F, and oxygen provided by good ventilation. Further advice: Do not pile more than 6 feet high and use a seed piece treatment.

If you are concerned about soft rot seed decay, proper soil temperatures during planting and shortly after are critical. There is a soil temperature “window” between 45˚ F and 55˚ F that favors the seed piece over the soft rot organism. If soil temperatures are below 45˚ F, the seed piece may not heal properly and soft rot can become a problem, especially if there is a rapid increase in soil temperature later. On the other hand, if soil temperatures are too warm at planting, say 60˚ F or above, soft rot development can become so rapid that the wound barriers cannot form fast enough to stop the decay process. Problems due to either of these temperature extremes can be even worse if the soil happens to be too wet, because the soft rot organism is favored by wet, anaerobic conditions. One of the worst combinations of factors is to place cold seed into warm, wet soil. This practice leads to condensation on the seed piece and another train wreck in the form of serious soft rot seed-piece decay.

Some other factors affecting seed performance are more straightforward. For example, any condition that accelerates the emergence of the shoots from the soil will help to establish a good stand for the new crop. With this in mind, it follows that both soil temperature and planting depth can greatly affect, for better or worse, the timing of plant emergence. Careful attention to planting depth can reduce the potential for diseases like soft rot and rhizoctonia, as well as help in the rapid establishment of a good, uniform stand.

Avoid the train wreck, do your best to plan ahead and be patient during the planting season. Good decisions about using certified seed, using effective seed piece treatments, planting at the proper depth and waiting for Mother Nature’s cooperation will help you get your potato crop off to a good start.”

75 Applewood Dr. Ste. A
P.O. Box 128
Sparta, MI 49345
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