Compiled by Vern Grubinger, University of Vermont Extension
(802) 257-7967 or

COMMON ARMYWORM ALERT (adapted from Cornell Extension)

Vegetable growers, particularly those who grow rye, other small grains, or sweet corn, need to be aware that there have been severe infestations of common armyworm this year in the northeast, from NY to Maine. In most years this pest is not a problem. However, this year is evidently an exception, so keep a closer eye than usual on your sweet corn plantings, and any vegetables near fields of rye or other small grains.  The pest is a caterpillar, and if you have an infestation you will see thousands of them.  They can be controlled with pesticides that are labeled for caterpillar pests on your crop. Options for many crops would include Warrior, Larvin, Sevin, or Bt. Reports indicate that Bt products containing the azawai strain are the most effective type of Bt to use against armyworms.

STRAWBERRY RENOVATION (adapted from article by Sonia Schloemann, UMass Extension)

Strawberry plantings grown in the traditional matted row system should be renovated after harvest for a number of reasons.  These include 1) to re-establish narrow rows, 2) rejuvenate the canopy, 3) interrupt disease buildup, 4) knock down insect and mite populations, 5) allow for effective weed control, and 6) stimulate runner production. For best results, renovation should be started immediately after the harvest is completed.  Ideally, individual fields or varieties should be renovated when picking is complete rather than waiting until all fields are ready.  The following steps describe renovation of conventional strawberry fields. (Many organic growers do not renovate fields due to the expense of hand weeding, but rather, re-plant after one year of fruiting.)

Annual broadleaf weeds can be controlled with 2,4-D Formula 40 at 2 to3 pints per acre in 25 to 50 gallons of water applied immediately after harvest. If grasses are a problem, sethoxydim (Poast) will control annual and some perennial grasses. But do not tank mix Poast and 2,4-D.

Mow the old leaves off a couple of inches above the crowns 3 to 5 days after herbicide application. Take care, especially in uneven fields, not to mow so low that you damage some of the crowns. Fertilize the planting with 20 to 40 lbs. per acre of nitrogen.  A second N application should be made in August to support fruit bud initiation. Be sure to do a leaf tissue analysis in August to evaluate the adequacy of your fertilization program.

Narrowing row width is important since wide rows lead to low productivity and increased disease pressure. Narrow rows have better sunlight penetration, better disease control due to improved air circulation, and better overall fruit quality.  Also, more berries are produced at row edges than in the middle.  The desirable row width at full canopy is 12 to 18 inches. This means that rows can be narrowed to as little as 6 inches during renovation. This can be done using a rototiller, rotovator, multivator or various cultivators. Work in the straw between rows and throw a small amount of soil over the row by cultivation. Strawberry crowns continue development at the top, and new roots are initiated above old roots on the crown, so ½ to 1 inch of soil should be cast over the rows to help with rooting. This also helps cover straw in the row and provides a good rooting medium for the new runner plants.

Soil compaction can result from tractor use and picker traffic in the field, especially on heavy, wet soils. Subsoiling between rows will help break up compacted layers and provide better infiltration of water. Subsoiling is best done late in the renovation sequence to minimize the interference of straw and crop residue.

Pre-emergence weed control should begin immediately after all cultivation and subsoiling is complete. Sinbar, Dacthal, or Devrinol are suggested materials. Check the product labels carefully. Devrinol must be incorporated by irrigation, rainfall, or cultivation to be effective. Rate and timing of Sinbar application is critical. If regrowth has started at all, significant damage may result.(see other precautions below)

Water is needed for both activation of herbicides and for plant growth. It is easy to forget to irrigate renovated strawberries when many other crops are grown on the farm. However, all the previous steps can be compromised if irrigation is overlooked. Don't let the plants go into stress. The planting should receive 1 to1-1/2 inches of water per week from either rain or irrigation.

For strawberry plantings at renovation, emerged broadleaf weeds can be controlled with 2,4-D (Formula 40) at 2 to 3 pts./acre applied immediately after the last harvest. Formula 40 is the ONLY 2,4-D formulation labeled for use in strawberries. Be extremely careful to avoid drift when applying 2,4-D.  If this application is delayed, some damage to strawberries is also possible. Read and under-stand the label completely before applying Formula 40.  If grasses are present at this time, sethoxydim (Poast) will control both annual and some perennial grasses.  However, do not tank mix Poast and 2,4-D.  Check the product label for rates and especially for precautions.  Strawberry plants should be mowed 3 to 5 days after the 2,4-D application.

Pre-emergence weed control should begin immediately after the plants are mowed and the soil is tilled to narrow the crop row. The most common practice at this time is to apply half the annual rate of terbacil (Sinbar at 4 oz/acre).  It is essential that the strawberry plants are mowed, even if 2,4-D was not applied, to avoid injury from Sinbar.  If regrowth of the strawberry plants has started, significant damage may result. Some varieties are more sensitive to Sinbar than others. If unsure, make a test application to a small area before treating the entire planting. Sinbar should not be used on soils with low organic matter, or on reportedly sensitive varieties such as Guardian, Darrow, Tribute, Tristar and possibly Honeoye. Injury is usually the result of too high a rate or overlapping of the spray pattern. If  Sinbar is not used, napropamide (Devrinol at 4 lb/acre) or DCPA (Dacthal at 8-12 lb/acre) should be applied at this time. Dacthal is again available for use in strawberries with the same label directions as on the previous label. Dacthal is preferred over Devrinol if the planting is weak. If Sinbar is used, napropamide (Devrinol at 4 lb/acre) should be applied 4 to 6 weeks later. This later application of Devrinol will control most winter annual weeds which begin to germinate in late August or early September. Devrinol should be applied prior to rainfall or it must be irrigated into the soil. During the summer, Poast can be used to control emerged grasses.

Cultivation is also common during the summer months. Cultivations should be shallow and timely (when weeds are small) to avoid root damage to the strawberries. The growth of strawberry daughter plants will also limit the amount of cultivation possible especially near the crop row.

Believe it or not, plant physiology is a very interesting subject! Strawberry growers incorporate many aspects of plant physiology into their crop production practices, especially at renovation time. Here are three basic concepts in plant physiology that relate to how the strawberry responds to management practices at renovation.

Source sink concept: Strawberry plant parts, such as leaves, roots, crowns, runners, flowers and fruit act as energy providers, (source) or energy users (sinks). Some parts, (i.e. crowns) may be switch for being energy users to energy providers, depending on the time of year. Competition for energy can occur between plants and within plants. When plants are too close together, they compete with each other for resources. You can expect yield per plant, and average berry size, to be reduced. In a matted row system, optimum plant density is somewhere around 6 to 8 plants per square foot of row. This is just a ballpark number and depends on variety, soil type, etc. Competition for resources within the plant occurs too. For example, flowering and fruiting processes compete with runner development. Runner development can compete with crown formation. Crowns can compete with each other. As a result, older, multi-crowned plants tend to produce smaller fruit. The optimum number of crowns in a strawberry plant is different for different cultivars. Growers using the plasticulture system usually aim for 4 to 6 crowns per plant.

During renovation of matted row plantings, growers use various methods to adjust plant density. Narrowing the rows back to 8 to 12 inches is the most common practice. Yields can be increased if narrower rows are combined with closer row spacings. The stand may be thinned during mowing or a light raking, which removes weakly rooted plants. Rows can be narrowed to one side so that original mother plants are eventually cut out. Or, a cultivator tooth can be used to cut out older plants in the middle of the row.

Root physiology: Strawberry plants must produce new roots to remain productive. Primary roots penetrate the soil and anchor the plant. Fibrous secondary roots form on the primary roots. These white roots mine the soil for nutrients and water and are frequently regenerated in a healthy plant. The root system of a strawberry plant is similar to that of an African violet. As the plant grows taller, it initiates new leaves. Older leaves at the base of the plant drop off. New primary roots develop where the old leaves fall off. These roots will not elongate unless they are in contact with moist soil. Root formation tends to take place when the plant is non-fruiting, and when soil temperatures are cool. Renovation can encourage new root development if rows are narrowed and a small amount of soil is added to the middle of the row. This encourages new roots to form at the base of the crown. Otherwise, as the plant grows older, the crown extends upward, grows out of the soil, fails to develop new roots, and is more exposed to winter injury.

Environmental interactions: In most June-bearing cultivars, cooler temperatures and shorter day lengths cause the plant to initiate flower buds for next year's crop. Different cultivars respond differently to these environmental triggers. Defining the exact conditions that cause fruit bud initiation to occur is like shooting at a moving target. It is generally believed the process begins as day lengths shorten to less than 14 hours. Short days (less than 14 hours) begin around August 7 in Harrow and August 15 in Ottawa. Flower initiation probably continues until cold temperatures cause plants to go dormant. These factors affect the timing of renovation practices. It is important to have a vigorous healthy plant in place when flower bud initiation begins.

(Mention of pesticides is for information purposes only; no endorsement of materials or brands is intended. Always read and follow instructions on the label.)