Gordon Johnson, Extension Vegetable & Fruit Specialist;gcjohn@udel.edu
Heavy rains after planting and cool temperatures have caused stand reductions in some sweet corn plantings. When stands are reduced, vegetable growers must decide whether or not to replant.
Replanting should only be done if the profit potential will be greater with the new planting. Considerations will include:
• Extra costs for seed and chemicals, planting cost, and labor cost
• Yield effects of later planting
• Delayed harvest and potential effects on following rotations or double cropping
• Herbicide issues and weed management in the replanted crop
The yield potential of the replanted crop must be high enough to cover the extra costs compared to keeping the crop plus at least 10% more profit potential.
Start with evaluating the yield potential of the crop with the reduced stand. There are often guides on how to evaluate reduced stands. Emmalea Ernest did a series of studies looking at yield reductions in processing sweet corn. She found the following:
“the varieties Overland and GSS 1453 were able to compensate for stand loss in terms of tonnage and, even more so, in terms of cut corn yield—even with population densities that were 40% of standard planting density. Of these two varieties, Overland had higher overall yields in the trials. SS Jubilee Plus also compensated well for reduced stand. Protégé compensated for stand loss up to 60% of standard population density, but produced significantly lower yields in terms of cut corn and tonnage at 40% of standard population density. GSS 2259P did not compensate for stand loss effectively and probably should not be used for early supersweet plantings where risk of stand loss is high. GSS 2259P produced its highest yields in terms of tonnage and cut corn at 120% of the standard population density (27,900 plants/A) which suggests that it should be planted at a higher density to obtain maximum yield.” See http://extension.udel.edu/weeklycropupdate/?p=5323 for more information
She also looked at gaps in stands and saw no differences in yield between evenly reduced stands and those with irregularly spaced gaps with lengths of up to 6.5 ft. Based on the results of these experiments, yield loss from stand reduction can be estimated based solely on plant population density, without consideration for unevenness in spacing if gap sizes are less than 6.5 ft.
Another important decision is delayed planting in following crops. Early crops can be double cropped after (such as early processing sweet corn followed by soybeans) and if replanted, this may eliminate double cropping potential or reduce double crop yields.
The following are replant considerations for different vegetable crops:
Processing sweet corn – for most varieties, replanting is not warranted unless stands drop below 50%.
Fresh market sweet corn – replanting is usually not economical but yield of marketable corn will be significantly reduced.
Lima beans – lima beans can compensate for stand reductions as much as 50%. Replanting rarely is recommended unless seed quality was very poor and remaining seedlings are of low vigor.
Snap beans – snap beans compensate for stand reductions of up to 50%. Replanting is not usually economical.
Pickles – cucumbers compensate for lower populations by increased branching and fruiting on branches. Yield reductions may be limited but once-over harvest scheduling is confounded by have more fruits of different ages on the plant. Replanting may be needed if stands are reduced by more than 35%.
Transplanted vegetables – replacement of dead, injured, or low vigor plants can be done up to a week after transplanting. Delays past that point will end up with too much light competition from older plants. After that point, consider replacing whole blocks, field sections, or row portions instead of individual plants.