How to Manage Pests
UC Pest Management Guidelines
Alfalfa is harvested more frequently in summer than in spring or fall when growth slows as a result of cooler weather. In California, many growers schedule 28-day harvesting schedules after the first cutting. However, there is considerable evidence that this might not be ideal. Decisions involving harvest timing, cutting height, windrow management, wheel compaction by harvesting equipment, and border harvesting can affect pest problems, as well as yield, quality, and profitability.
Usually, the choice of harvest time represents a compromise between the customer's demands for quality and the grower's desire to maintain high yields and a vigorous stand. The highest quality of alfalfa is low in fiber and high in digestible protein and total digestible nutrients. The best time to harvest alfalfa to maximize quality is from very young vegetative stages to early bud stage. However, cutting at these early growth stages produces low yields and can greatly weaken alfalfa stands; the plant does not have sufficient time to replenish carbohydrate and protein root reserves. Harvesting after the plant has had the opportunity to replenish root reserves increases yields and significantly improves health and competitive ability of the alfalfa stand. The benefits of long cutting schedules are often carried over from season to season.
Although there are clear economic incentives for growers to produce early harvested, high-quality forages, repeated early stage cutting schedules can be devastating to alfalfa persistence, growth, and yield and lead to severe weed infestations. Thus, it is important to allow several 'long' cutting intervals over the year to allow sufficient replenishment of root reserves, to maintain high yields, and for continued health of the stand. It is recommended that growers consider 'staggered' approaches to cutting schedules by alternating 'short' (e.g. 26-day) with 'long' (e.g. 35-day) intervals over the season. Some harvests could be cut early for quality, and a subsequent harvest would be cut late for high yields and stand health. Precise cutting schedules are difficult to recommend because the growth rate of alfalfa depends on location and time of year.
Early harvest may be a good strategy to avoid further damage when alfalfa crop has a high (late) infestation of alfalfa weevil in spring, or Lepidoptera (caterpillar) damage in summer and can help avoid an insect spray. After harvest however, growers need to monitor fields carefully to detect early damage the young shoots, which can be devastating to the following regrowth.
Ideally, the last harvest of the season should be early enough to allow plants enough time to build up reserves before the first frost, although this is not critical in more southern regions where frosts are later or nonexistent. Sufficient canopy coverage is important to suppress winter weeds. However, dense winter canopies can lead to high Sclerotinia infestations, and clipping (even late fall clipping) is an important management tool when conditions are right for Sclerotinia.
UC IPM Pest Management Guidelines: Alfalfa