Tuesday, April 3, 2012

Successful Alfalfa Establishment

Rory Lewandowski, Extension Educator Wayne Co. and Crossroads EERA

April is a good month to plant and establish a new stand of alfalfa. The earlier in the month planting is done, the better. Once an alfalfa plant has germinated, that new plant needs between 6 to 8 weeks to get a good root system established that enables it to handle warmer and drier summer weather. At about 8 to 10 weeks after emergence the alfalfa plant pulls the growing point below the soil surface. This process is called contractile growth. Once contractile growth occurs the alfalfa plant is considered a true perennial. The protected growing point below the soil surface is the reason why the alfalfa plant can survive winter temperatures, close cutting and grazing.
Some of the most common questions regarding successful alfalfa establishment include soil fertility, planting depth and weed control. All three factors need to be addressed to successfully establish an alfalfa stand. The basis for any decisions regarding the application of lime, phosphorus and potassium fertilizer is a soil test. The recommended soil pH for an alfalfa stand is 6.8. Remember that it takes 6 to 9 months after lime is incorporated and mixed into the tillage zone before the target pH is reached. If soil pH is below 6.5, it is probably a wise decision to apply lime this spring and aim for a late summer planting. A soil test can also help determine if phosphorus and/or potassium needs to be applied before planting. Phosphorus is a critical element to aid a new plant in establishing a good rooting system. The point here is that lime and fertilizer can represent a significant dollar investment and guessing as to the need and quantity can be expensive. So, as the saying goes; “Don’t guess, soil test”.
Weed control in an alfalfa stand really needs to begin before the crop is planted. Herbicide options in an established alfalfa stand are limited. Perennial broadleaf weeds and grasses should be managed and controlled in the crops previous to the alfalfa rotation. The general rule of thumb is that at least 95% of the weed control in a forage crop is provided by developing a dense, healthy stand that will not allow weeds to invade.
Just like other agronomic crops, weeds that emerge with the new alfalfa seedlings are the most destructive. The goal should be to maintain the new seeding relatively weed free for the first 60 days. These factors often make it necessary to use an herbicide with a pure seeding of alfalfa. There are a few herbicides that are commonly used when establishing a pure stand of alfalfa. Balan or Eptam can be used as pre-plant incorporated herbicides to provide control of annual grasses and some broadleaf weeds. Butyrac and Bromoxynil can be used to provide early post emergent control of some broadleaf weeds when weeds are no more than 2 inches tall. Clethodim and Sethoxydim or Sethoxydim plus Dash can control annual and perennial grasses in alfalfa. Prowl H2O provides residual control of most annual grasses and certain broadleaf weeds, but must be applied prior to weed emergence and the seedling alfalfa must be in the at least the 2nd trifoliolate stage of growth but not more than 6 inches tall. Imazethapyr and Imazamox control annual broadleaf weeds and suppress or control grass weeds, and must be applied when alfalfa is in the 2nd trifoliolate state or larger and when weeds are 1 to 3 inches tall or when rosettes are no more than 1 to 3 inches wide. More details are available in the 2012 Ohio and Indiana Weed Control Guide. Take the time to read and follow label directions. Herbicide use on forage crops such as alfalfa can involve harvest and grazing restrictions, in addition to specific limitations regarding the timing of the herbicide application.
Incorrect planting depth has been responsible for many poorly established stands of alfalfa or seeding failures. Alfalfa is a small seed and should not be seeded too deep. The recommended seeding depth for alfalfa is one-quarter to one-half inch deep. It is better to err on the side of planting shallow rather than too deep.
Another factor that works hand in hand with planting depth is correct calibration of the planter for seeding rate. The Ohio Agronomy Guide recommends seeding alfalfa at 15 lbs/acre of pure live seed for a pure stand. If a coated alfalfa seed is used, be aware that coatings can account for up to one-third of the weight of the seed. This can affect the number of seeds planted if the planter is set to plant seed on a weight basis. Seed coatings can also dramatically alter the flowability of the seed through the drill, so be sure to calibrate the drill or planter with the seed being planted.
Finally, use fungicide treated seed to provide protection against seedling diseases and make sure the seed is planted with the proper bacterial inoculum that has been maintained under conditions that ensure the inoculant is viable.