Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
Fall planting season for plasticulture strawberries is approaching in September. Growers who root their own tips will need four weeks depending on tray size. While 72 cell trays root faster, plants grown in 50 cell trays will be larger and will grow more quickly after transplanting. Rooting tips requires misting for several days while roots are established. Growers who buy plug plants should have already put in orders as nurseries only root limited amounts over what they have orders for.
The main source for strawberry tips that growers or nurseries root for fall plasticulture planting in the Eastern US has been Canadian nurseries. In 2012 there was a problem with viruses in one nursery source that a number of Delmarva growers received. Efforts have been made to reduce the potential for viruses in the source tips. Ideally, a tip producing nursery should receive virus free foundation material, increase that material by tissue culture and then increase in the field for a minimum of generations to take tips. Attention needs to be paid in tip growing areas so that enough rotational ground is available to avoid recontaminating the planting stock with viruses and tip producers should have a vigorous testing program for viruses. The take home message is know your tip source or ask the nursery you are working with for plug plants about their tip source.
Strawberries are very prone to root diseases. This is why, in major strawberry producing areas, fumigation has been a common practice (along with weed control). Fumigated strawberry beds almost always are higher producing than non-fumigated areas. There has been extensive research on fumigation alternatives to methyl bromide which is being phased out. Other chemical fumigants are still available but are somewhat less effective. Use of special plastic mulches that retain fumigants – virtually impermeable (VIF), or totally impermeable (TIF) mulch films – have improved fumigant effectiveness and reduced setback restrictions. However, these mulches will keep fumigants in the soil for a longer period making in necessary to have longer plant back periods in some cases. When using such mulches with available fumigants, make sure to follow manufacturer’s recommendations for waiting periods between fumigation and planting. The following site at the University of Florida has a good overview of research with these mulches http://edis.ifas.ufl.edu/in403.
For small growers who don’t want to use fumigation, do not have the capability for fumigation, or can’t meet setbacks, there are some alternatives. One of the more promising has been mustard seed meal incorporated prior to laying the plastic. While fairly costly, it does provide some fumigation action and also is a nitrogen source. Another alternative is to grow a crop of sorghum/sudangrass prior to the strawberry crop then chopping it and tilling into the soil. This should be done several weeks ahead of time also (it will take 4-6 weeks to grow the crop).
We still do not have many choices for varieties that work in our region. The majority of our plasticulture strawberries have been Chandler with some Sweet Charlie for extended (early and late) production. In discussions with Barclay Poling (NC State) last week, he stated that the North Carolina industry is largely planting Camarosa now. Experience in our region with Camarosa has been mixed in the past. However, after listening to Barclay, I would suggest that growers try more Camarosa on Delmarva. The key with Camarosa is that it needs to be planted earlier than Chandler. Camarosa has the potential to give longer production seasons than Chandler and will out-yield Sweet Charlie. While in the past we have thought of Camarosa as a shipping berry, Barclay stated that it is the most popular direct market berry in North Carolina now.
On the Chandler variety, planting date is so important. Target the first 2 weeks in September. Later plantings will not yield as well. However, research has shown that early row covers, while not increasing crown number, can increase flower number if Chandler is planted later and compensate somewhat for the losses. Adequate fall crown number is important with Chandler. However, early planting may produce too many crowns and lead to smaller berries next year.
I think there is great potential to replace some of our Chandler production with 2 day-neutral varieties: Albion and San Andreas. Both have excellent berry quality and when planted in the fall like Chandler will produce good spring crops (will start earlier than Chandler) with extended production into early summer. I have found the trick with Albion is to plant at a higher density. This is a variety that can be planted with 3 rows per bed, or with in-row spacing down to 8-9 inches. Both also give some potential for fall production in the planting year or the following year. For first year fall production, planting as early as possible is recommended.