by Tamara Scully
As early autumn’s colder weather settles in, strawberry growers utilizing a plasticulture system are busy with fall planting of plugs into raised beds. Depending on climate, the exact timing of planting strawberry plugs each autumn varies, as the berries will need time to establish themselves before growth is stopped by cold weather.
In a recent Virginia Cooperative Extension webinar, Dr. Jayesh Samtani, small fruit Extension specialist, that the increased temperatures associated with climate change has impacted how late into autumn strawberry planting can occur.
Establishing strawberry plants in a plasticulture raised bed system allows for crown development on newly planted plugs before the winter cold inhibits growth. The goal is to have one to two branch crowns developed prior to dormancy. Strawberries require temperatures of 50º F, which is the base temperature at which they will grow, to continue developing.
Fall-planted strawberry plugs can benefit from the use of row covers to extend the autumn growth period, and row covers can provide other benefits throughout the cold weather months. Prior to using row covers, consulting the long range weather forecast is recommended.
“In order to really use row cover applications in the fall, you have to understand what kind of weather you will be facing in the coming few days,” Samtani said. “Depending on the situation, a lot of growers may not think that row covers are the best use of their time in the fall. It does take labor to put that down.
Growing degree day (GDD) calculations add together the high and low temperatures each day, and then divide that sum in half to determine the mean daily temperature. If the mean temperature is above the crop’s base temperature, then each degree above that base level is a GDD. The days are cumulative.
Depending on the strawberry variety being grown, GDD can vary. Chandler, an old standby, only requires 650 GDD to mature. Other popular varieties can require 800 GDD. Growers in colder climates can select cultivars with lower GDD requirements. And row covers can be utilized to enhance GDD by creating a microclimate with higher temperatures.
Because row covers retain heat, they add GDD, providing the fall-planted crop extra time to grow and allowing for enhanced root development. If planting is delayed, or if the plugs being planted have poorly developed root systems, an autumn row cover can enhance crop establishment and increase spring productivity.
Row covers can also add protection from cold temperatures in winter and be used in spring to protect buds and flowers from frost. For growers who opt not to use row covers to promote fall branch crown development, row cover use in winter and spring can still bring benefits.
Once the mean daily temperature drops below 50º, strawberry crowns go semi-dormant and do not actively grow. Depending on how cold the winter is, row covers can be left on until spring. But in regions where the winter temperatures are mild, leaving row covers on all winter could promote flowering and fruiting, putting plants in more danger of damage from spring frosts.
“You probably don’t want the row covers to stay on for the rest of the winter, because you’re increasing the temperature in the microclimate, and the plants may not get very well acclimated to the cold environment,” Samtani said. “And then you don’t want to advance the plant too far ahead.”
Row covers can also create an ideal habitat for spider mites. It is advised that growers regularly check under covers to scout for these pests. Plant tissue could have decreased cold tolerance if row covers are used in winter and unseasonably warm temperatures occur, followed by another cold snap. And the humidity that can build up under the covers when it’s rainy and sunlight levels are low can promote diseases – such as powdery mildew – to develop.
Broadleaf and other weeds are also more populous when using row covers and can be treated with herbicides. Weeds in planting holes should be hand-pulled.
Freeze events are also a concern even when row covers are used. Depending on plant growth stage, the weight of the row cover and the temperature under the row cover, precautions against frost need to be taken.
Row covers range from lightweight to heavyweight. Each offers protection from cold temperatures, and as protection levels increase with heavier fabric construction, the light levels which can permeate the covers decrease. Lightweight covers allow 85% light penetration and protect crops down to 27º. The heaviest allow only 40% of the light to be transmitted but protect crops in temperatures down to 18º. More than one row cover can be used for added cold protection. Row covers can also protect against moisture loss and desiccation. “There’s pros and cons that come with row cover applications,” Samtani said.
Diseases in Plasticulture Strawberries
Dr. M. Mahfuz Rahman, West Virginia University Extension plant pathologist, discussed diseases of concern in newly planted plasticulture strawberry beds. When plugs are planted in autumn, disease symptoms may not be noticeable. Latent disease can then erupt when the plants are maturing, damaging the crop.
Two diseases of concern are Anthracnose crown rot and Phytophthora crown rot. These can be distinguished from one another by examining the crown, which will be a marbled brown and red if Anthracnose crown rot is the culprit, or a dull brown if it’s rot caused by Phytophthora.
“Many of these infections can come in on the plants,” Rahman stated. “But these are latent infections. These are symptomless at this time.”
A newer disease of concern is Pestalotia blight, which causes leaves to look scorched as they desiccate from the fungal infection. It can eventually kill the whole plant. The fruit can also have disease symptoms. It can be treated with fungicides. Highly infected leaves should also be removed in autumn and early spring.
For growers who are fall planting strawberries into a plasticulture system, management of diseases early on can be an effective tool and is possible.
With the use of row covers in plasticulture, fall-planted strawberries can receive benefits from temperature moderation to protection from browsing deer to frost protection. Knowing which row cover weight to choose, selecting the appropriate time to apply the covers to meet your growing goals and monitoring for pest and disease under the row covers can be a fruitful way to enhance productivity for your next berry season.