Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
September is when plasticulture strawberries are planted on Delmarva. Plug plants grown from strawberry tips by nurseries and greenhouses in the region are most commonly sourced by growers. Northern grown tips from Canadian nurseries often are used by plug growers to reduce diseases such as Anthracnose. While nurseries and plug growers are diligent in producing quality planting material, at times, problems can arise. In addition, planting practices can greatly influence the success of the planting. The following are some considerations to be successful with plasticulture strawberry establishment.
Plug Conditions
When receiving plug plants, growers should inspect for plug conditions. It typically takes 4 weeks for tips to root but this depends on the growing conditions and tip condition. If tips are not fully rooted then the plugs will not pull properly and roots can be damaged in transplanting. In contrast, root bound transplants may dry out and be difficult to water. If dry plugs are transplanted they have a high probability of dying after transplanting. Blank plants that do not have a crown should be discarded and not planted
Diseases and Mites
Nurseries and plug growers seek to produce disease-free plants. However fungal diseases such as Anthracnose can be brought in on plants. More difficult to detect are viruses. Inspect plants for virus symptoms such as abnormal leaf color, mottling, curling, or leaf distortions. Suspect plants should be sent to disease diagnostic laboratories for testing and should not be planted. If any plants appear to be weak, cut through a few of them, and look for signs of discoloration in the crown. Reddish or reddish-brown tissue is an indication of anthracnose crown rot, phytophthora crown rot, or the more recently identified foliar and crown disease Pestalotiopsis. Growers should also inspect plants for mites and treat with a miticide prior to planting if detected.
Planting Depth
Strawberry plugs are very sensitive to planting depth – too deep and plants will die, too shallow and plants will dry out. Plugs should be placed so the plug is fully in the ground up to the crown, firmed with the surrounding soil, with no part of the plug exposed and with no soil covering over the crown.
Water
Growers in plasticulture with drip irrigation often will try to irrigate bed before planting so they are fully saturated. This is not possible in our sandy soils with a single drip line in the middle (double lines will have more fully wetted soil). In addition, there is a risk of leaching nitrogen out of the strawberry root zone. It is preferred to add water during transplanting and then overhead irrigate a few hours for several days to establish plants until roots can reach wetted areas from the drip tape.
Fall Fungicides
With wetter, warmer fall weather conditions and the use of overhead irrigation in establishment, there is a risk of foliar and crown diseases. To control phytophthora in susceptible varieties, apply mefenoxam through the drip system 15 days after planting followed up with foliar applications of a phosphite product (Phostrol, Prophyte, etc.) 2 to 3 weeks later.
If anthracnose crown rot or Pestalotiopsis is suspected, captan and Switch both have good efficacy and should be applied 2 or 3 times during the fall being sure to get good coverage into the crown area.