Strawberries

With the majority of freezing night time lows behind us, strawberry growers should begin scouting for pests during bloom. Earliglow is already in bloom on the Lower Eastern Shore and other cultivars will soon follow with the warm weather forecasted for 4/12-4/16. Be on the watch for spring pests during bloom including thrips, tar-nished plant bug, leafrollers, aphids, leafhoppers which begin attack plants during flowering in Maryland. Author: Haley Sater; Title: Spring Pest Scouting in Strawberries

Southern blight is a fungal disease that is most common in the tropics and subtropics, but also is found in the SE United States in the summer. In Maryland we usually find it in the southern part of the state in counties like St. Mary’s, Charles and Wicomico. It has been found this year in more northern counties such as Frederick, Montgomery and Baltimore.

This is a quick note to say that after looking at some strawberry fields in which the transplant plugs were wilting it at first looked like there could be some root disease problem.

It has been an unusually cool April, especially the last 2 weeks. This is following a warmer than average March. If you have strawberry plants starting to flower the flowers are going to be susceptible to cold damage during one of our chillier nights.

Over the last few weeks I have been sent pictures of and have seen dark spots on the foliage of strawberry plants (figs. 1 and 2). These spots can look pretty bad at times and are thought to possibly be the start of some disease such as angular leaf spot or anthracnose. The dark spots are usually on the upper or lower surface of the leaf, but at times can be found on both surfaces of a leaf.

Tarnished plant bug (TPB) (Lygus bug) adults are about ¼ inch long, oval, flattened, yellow to greenish brown, and have dark markings on their wings. The immature forms are pale green. There are 3-5 generations of this pest each year. Adults become active in early spring and lay their bow-shaped eggs into stems, and leaf midribs. Egg hatch takes place about a week later, and the green-yellow nymphs develop through 5 instars, reaching the adult stage in approximately 30 days.

The production of strawberry plugs involves multiple stages during which pathogens can infect the plug plants before they are distributed to growers. Despite regular scouting by propagators, and chemical sprays applied to avoid diseases, these infections can sometimes be latent and asymptomatic (i.e., they are present in the plant material, but there are no outward symptoms), making them a challenge to identify and manage.

While visiting some strawberry fields over the last few weeks, I ran into a few areas that had two spotted spider mite (TSSM) feeding. These were mostly in fields that had been using row cover. Spider mites Tetranychus urticae are well adapted to high-temperatures and can complete their life cycle in as little as 7 days when temperatures are > 80º F. The temperatures under row covers in the early part of our season were much above normal and rainfall was below normal leaving conditions hot and dry, which permitted spider mites (if present) to develop quickly. Warm dry conditions along with the nitrogen content of leaves greatly influence TSSM reproduction rate. Applying excessive nitrogen favors spider mite outbreaks.

I visited some strawberry fields over the last few days in Maryland. Most of the strawberry fields were on plastic but some were matted row production and a few in high tunnels. With the cooler weather we have had of late I was surprised to still find low levels of mites in the fields, with a few hot spots of mites in some high tunnels. There was only one species of mite found: the two spotted spider mite, Tetranychus urticae.

Cyclamen mites have been found in a few mid-Atlantic strawberry fields as well as more widespread to the south of us in North Carolina. So once we start to really warm up they may become more of a problem along with two spotted spider mites.