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Giving Your Alfalfa Stand the Winterizing Treatment

posted by Horse Owner Today    |   August 23, 2013 16:21

Alfalfa field March 21, 2014

Photo credit:  Bonnie Newton

Alfalfa field, one month after first cut.

If not properly managed, alfalfa can suffer winter injury or winterkill. Several factors play into good winter survival of your alfalfa stand.
Taking a Second Cut
For alfalfa, early fall is a critical time as plants are storing nutrients needed to survive the upcoming winter. Cutting plants during this period adds double the stress to the plants as they have to expend energy for regrowth as well as nutrient storage. During a minimum of six weeks after cutting, alfalfa plants need good growing conditions to ensure sufficient regrowth and energy storage to support winter survival. Plants harvested after August 15th may not have six weeks before a killing frost and may be susceptible to winter kill. A killing frost is considered minus five degrees Celsius or lower. Harvesting after a killing frost does
not affect food reserves but reduces the amount of stubble which helps trap snow. The trapped snow provides an important insulating blanked for alfalfa crowns.
Fertility
If alfalfa makes up 50% or more of the production in the stand and was properly inoculated at seeding, nitrogen is generally not a concern in the forage stand as the alfalfa will fix the nitrogen required by the stand. Phosphorus, potassium and sulphur are the three nutrients which should be considered in stands with large proportions of legumes. Phosphorus and potassium are particularly important as they support root and nodule health and over-wintering capability. Both of these nutrients can be fall applied as they are relatively immobile in the soil and will not leach or volatilize to the atmosphere like nitrogen. The most cost-effective way to maintain adequate soil fertility is to do a fall soil test.
Stand Health
An otherwise healthy stand can be impaired by insects and disease such as alfalfa weevils and downy mildew. Scouting for insects during June is important in noticing and minimizing insect feeding damage while disease resistant alfalfa varieties are your best defense against various root and leaf diseases.
Environmental Factors
Not all factors in alfalfa fall management are under your control. For example, wet soil conditions in the fall can reduce the plants ability to harden prior to winter. Lack of snow cover is also a concern as alfalfa crowns can be exposed to extreme cold. Snow cover can be improved by leaving sufficient stubble height.
Planting cold tolerant and disease resistant varieties along with a good fertility program and careful cutting management will help winterize your alfalfa stand for better longevity and productivity.
For more information on this or other topics please call me at the Watrous Ministry of Agriculture office (306) 946-3219, the Agriculture Knowledge Centre at 1-866-457-2377 or visit our website http://www.agriculture.gov.sk.ca/

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Fall Feed Management

ALFALFA PRODUCTIVITY AFFECTED BY PESTS AND ENVIRONMENT

posted by Horse Owner Today    |   July 23, 2012 17:51


BY MICHEL TREMBLAY, PAG.
PROVINCIAL SPECIALIST, FORAGE CROPS

The 2012 growing season has been characterized by significant rainfall across the agricultural zone of Saskatchewan, following a dry, warm winter. In Saskatchewan, spring precipitation is the largest single determinant of yield of cool season forage species. With favorable soil moisture present in nearly all areas of the province, a good forage crop should be expected. Some producers have noticed that their alfalfa fields are not yielding, considering the soil moisture present. The following factors may be contributing to decreased alfalfa vigor and yield.
Alfalfa weevil
The alfalfa weevil (Hypera postica) is a pest of alfalfa crops, and is increasing in occurrence in Saskatchewan. Alfalfa weevils have been observed predominately in the southeastern and east-central parts of the province in alfalfa hay and seed fields. Adult weevils are approximately 5 mm in length, brown in colour, with a darker brown stripe from the head running down the back. The alfalfa weevil is a snout beetle, with a pronounced hook shaped proboscis at its anterior end. The larvae, when newly hatched, are yellowish green. At maturity, larvae are approximately 8 mm in length, and have a black head and a white stripe down the centre of its back. Adult weevils overwinter under plant debris and soil in and around alfalfa fields. Weevils emerge in spring and begin feeding on alfalfa leaves, creating round holes in the leaves. Females, when ready to lay eggs, chew a hole in the stem of the alfalfa plant and deposit from one to 40 eggs per stem. The bright yellow eggs can be seen with the naked eye if the stem is cut open. Eggs hatch one to two weeks after being laid, and the emerging larvae initially feed within the stem before moving to the developing buds, then newest leaves.

 

Alfalfa weevil larvae leaf damage.
Source: Saskatchewan Agriculture

Damage begins as pinholes and progresses to extensive feeding damage to leaf surfaces between veins, resulting in a ragged, skeletonised leaf. Heavily infested fields may not have flowers present, as the larvae will remove developing inflorescences. Often the first sign of weevil damage is the discoloration of the crop as the larvae feed. Evident from the field edge, the crop will develop a whitish sheen, or frosted appearance, due to foliar damage.

 

Alfalfa weevil larvae.
Source: Saskatchewan Agriculture


Larvae feeding occurs predominantly early in the season, in mid-June to mid-July. Mature larvae move down to the base of the plant or onto the soil and spin a lace-like cocoon. The adults emerge from the cocoon in one to two weeks. The larvae represent the most destructive stage of the alfalfa weevil life cycle, and most weevil damage occurs on the first cut. Usually a single generation of the weevil occurs per season in northern climates.
The most cost effective control can be cultural. Cutting when the potential for significant weevil damage becomes apparent will stop yield losses. If the infestation is severe and early cutting is not feasible, alfalfa weevils can be controlled by using insecticides as per economic thresholds indicated below.

Economic thresholds for alfalfa weevil pesticide application

Seed:
Foliage: 35-50 per cent of foliage tips show feeding damage.
Larvae: 20-30 3rd/4th instar larvae per 90o sweep of insect sweep net.

Hay:
30 cm crop height and one larva per stem.
40 cm crop height and two larvae per stem.
Three larvae per stem requires immediate action regardless of height of crop.
Two or more active larvae per crown (four to eight larvae per sq. ft) on regrowth after the first cut.

 

 

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Feed

Fall Management of Perennial Forage Stands

posted by Horse Owner Today    |   September 1, 2011 17:51


Charlotte Ward, MSc, PAg – Regional Forage Specialist - Yorkton

 

The typical production schedule for a perennial forage crop usually consists of 3 to 5 years of high yield (honeymoon period) followed by a rapid decline in productivity. Once this 3 to 5 year honeymoon period is over, factors such as declining soil fertility and decreasing plant numbers typically result in lower production. Another key factor that will affect long-term stand productivity is timing and frequency of harvest – whether or not producers take a 2nd cut of hay or grazing and the timing of that harvest.

Proper management of these stands from now until freeze up can help to mitigate the natural decline in productivity.

How can soil fertility affect stand productivity and why should be thinking about it this fall?

As we harvest perennial forages and remove the plant material from the field, we are also removing a tremendous amount of nutrients from the soil as well. High yielding forages will remove more nutrients than low yielding forages, which will in turn likely remove more nutrients than if the stand were grazed. Over time we need to replenish these nutrients. Manure, commercial fertilizer and even feeding livestock on the field can all be used as tools to import nutrients.

If alfalfa makes up 50% or more of the production in the stand and was properly inoculated at seeding, nitrogen is generally not a concern in the forage stand as the alfalfa will fix all the nitrogen that the stand needs. Phosphorus, potassium and sulphur are the three nutrients that we tend to focus more on in stands that contain a significant portion of legumes as legumes are high users of these nutrients. Phosphorus and potassium are of particular importance as they contribute to root and nodule health and the over-wintering capability of the plants. Both of these nutrients can be fall applied as they are relatively immobile in the soil and they will not leach or volatilize to the atmosphere like nitrogen will. Fall application of these nutrients can also help to decrease the work-load next spring. The most cost-effective way to know where your stand is at in terms of soil fertility is to do a fall soil test.

How does the timing of harvest and frequency of harvest affect forage yield?

Improper cutting of alfalfa stands can lead to winter kill. Understanding alfalfa physiology can help to avoid this problem. In the plant, energy is produced in the leaves through the process of photosynthesis and is used to fuel plant growth. As the plant produces excess energy, it is stored in various plant parts such as the roots and crown. The stored energy is used for regrowth following cutting, plant maintenance over winter and growth during early spring.

When an alfalfa plant is cut, few leaves remain and the plant may draw on stored energy reserves for regrowth. Generally the plant will need 6 weeks to replace leaves and replenish stored reserves to pre-cutting levels. Thus there is a 6-week critical period after cutting that the plant needs to ensure that it has good energy reserves going into winter. This is of particular importance to producers looking to take a second harvest off their fields, either through mechanical harvest or grazing livestock.

Plants harvested after August 15th may not obtain six weeks of good weather of replenish reserves before a hard frost and can go into winter with low energy levels. Plants with low energy levels are more susceptible to winter kill. If it is necessary to take a second harvest, producers should wait until after a killing frost as the plants will shut down and will not try to mobilize energy reserves.

Fall harvests should be approached with caution as harvesting plants after August 15th reduces the stubble height of the field which is important for trapping snow and spring moisture next year. Standing alfalfa will not only trap snow this winter, but will also cover the soil next spring and summer to minimize moisture lost through evaporation.

What can producers do this fall to optimize forage yield next year?

·        Avoid cutting between August 15th and the first killing frost

·        Ensure there is adequate soil fertility, including phosphorus and potassium which is        particularly important for root health and development as well as nodule health

·        Manage stubble for maximum snow cover