Vegetables

Fruit and Vegetable News, Volume 12, Issue 2 (May 13, 2021)

Expect two-spotted spider mites on vegetables with hot and dry weather.

I have gotten reports from flower growers of an inundation of thrips into their flower crop in the last week or so. I know, I know flowers are not vegetables, but many of the Flower thrips species that get into flowers will get into and on vegetables. Thrips are tiny, thin yellowish-orange insects the size of metal filings with fringed wings.

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.

Over the past few weeks we have seen several greenhouse (GH) and high tunnel (HT) vegetable (basil and tomato mostly, but also lettuce, pepper and spinach) operations from around Maryland having problems with thrips.

The hotter temperatures we have had have caused thrips and to a lesser extent two spotted spider mite, TSSM (Tetranychus urticae) populations to rapidly increase in some vegetable fields. These pests feed by puncturing the outer layer of plant tissue and sucking out the cell contents, which results in stippling, discolored flecking, or silvering of the leaf surface (fig.1).

Over the last three months a few early season high tunnel operations on the Eastern Shore were having problems with some of their seedlings and leaf crops. Crops like spinach would have ‘whitening’ and then browning and eventually dead margins of their leaves while seedlings would collapse. The problem was found to be ‘red legged winter mites’ Penthaleus dorsalis, which is a new pest in vegetables and herbs for us (fig 1).

This week I saw several high tunnel tomatoes and cucumbers with moderate to severe two spotted spider mite (TSSM) Tetranychus urticae infestations (fig. 1). These pests vary in color from white to yellow to red. Mites feed by sucking chlorophyll from the plant, which at first appears as small white or yellow marks on the top surface of the leaf (fig. 2). This damage may look like other problems early on and because the mites are difficult to see on the underside of the leaf at this stage of damage their build-up can go unnoticed. The feeding damage then progresses to loss of chlorophyll, yellowing, browning (fig. 3) and eventual death of the leaves or whole plant.

Thrips are a major problem for vegetable and flower growers throughout the United States. In the past 10 years, some species (in particular, western flower thrips (WFT)) have caused increasing problems. Symptoms of thrips damage include scarring and/or deformation of the leaves and fruit (Figs. 1-3). Additionally, certain thrips species can damage vegetables by vectoring viruses such as Tomato Spotted Wilt Virus (Figs. 4-5). However, some symptoms that appear to be thrips-induced can be caused by environmental or varietal factors and this can lead to increased applications of pesticides when they were not necessary.

I visited some strawberry fields over the last few weeks in Maryland and while most of the fields were on plastic, some were matted row production. Overall I found low levels of mites in most of the fields, with a few hot spots.