Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
One of the most difficult decisions that vegetable growers and advisors have to make is when to replant vegetables with stand problems. Often we have little research base to go on in regard to these decisions and it becomes more of an educated guess. I have heard many anecdotes of fields with reduced stands that have yielded well.
There are many reasons for reduced stands – insects, birds, planter problems, soil crusting, herbicide damage, and seed quality problems to name just a few. Before you even consider replanting, make sure that you diagnose correctly what caused the stand reduction. If the problem is repeated you will have lost money twice.
A replanted field should have a high probability of increased yield potential compared to the stand being replaced. That yield increase needs to cover the cost of replanting (seed, herbicides, additional fertilizer, tillage, equipment costs, etc.) and any other opportunity costs such as lost potential for double cropping. Consider issues such as increased pesticide needs in later plantings (replanted sweet corn will often require more sprays for insect control for example). With processing vegetables, you need to work closely with the processor to see if rescheduling is possible. They may have already filled later acres or be beyond their cutoff dates for that crop for example. With fresh market vegetables, consider how replanting will affect your markets and the prices that will be obtained for later crops versus a partial early crop.
A major difficulty is evaluating the yield potential of the existing stand. This is further complicated in processing vegetables that are once-over harvested where stand variability may lead to difficulty in scheduling for peak quality. Where research on replanting vegetables is available for this region, use that as a guide. Crop insurance providers often have access to information on replant yields and should be consulted where crops are insured.
Many crops compensate well for lower populations. Lima beans are a good example. Stand reductions as much as 50 % result in little relative yield loss in lima beans. In general, vining crops and indeterminate crops compensate well for reduced stands as do crops that branch strongly. Some leafy vegetables such as greens can also compensate for low stands by producing larger leaves. Bush type vegetables with limited branching, determinate types, and vegetables that produce one harvestable plant part per seed or transplant will be less able to compensate for stand reductions. Consider the variety also. For example, many sweet corn hybrids will produce a harvestable second ear at lower populations and thus will compensate for reduced stands.
Also consider the vegetable type. For example, supersweet sweet corn varieties have a wider harvest window than normal sugary types and therefore irregular corn stands with variability in maturity can still be harvested with not much tonnage loss. Consider how later replanted fields might be affected by heat or cold. Replanted snap beans exposed to summer heat will have reduced yields; in contrast, later planted lima beans may be exposed to cooler temperatures at flowering and have higher yield potentials.
There certainly will be times where replanting a vegetable field is necessary and replanting makes economic sense; however, more often than not you will make more money by taking the partial stand to harvest.