Mites/Miticides in High Tunnels

We are beginning to get some reports of spider mites on tomatoes in high tunnels. Mites are challenging pests to manage in greenhouses and high tunnels as they often go undetected when their populations are low. However, they reproduce quickly and hot spots soon become common throughout structures. Unlike other high tunnel pests, there are no traps for mites, so growers must regularly examine leaves, particularly the undersides.

When mites are found in high tunnels, there are  several miticides available for  vegetable crops. These materials need to be managed appropriately because:

  • There are limitations on the number of uses in structures
  • Mite populations can become resistant to miticides that are overused
  • Some miticides are effective against only certain species of mites.

Because of this, regular weekly monitoring becomes the backbone for mite management.

Common Mite Species

Tomatoes are very susceptible to mites and there are  two common mite species that we scout for routinely: tomato russet mite and  two-spotted spider mite.

Tomato Russet Mite

Since 2009, tomato russet mite (Figure 1) has become one of the more common pest problems on high tunnel and greenhouse tomatoes. Because russet mites are difficult to find when scouting, look for their damage.  Early signs of damage include either appearance of small russeted fruit or bronzing to plant stems (Figure 2).

Figure 1. Tomato russet mites are much smaller than two-spotted spider mites. (Photo: Ric Bessin, UK)

Figure 1. Tomato russet mites are much smaller than two-spotted spider mites. (Photo: Ric Bessin, UK)

Figure 2. A fruit damaged by tomato russet mite and characteristic stem bronzing. (Photo: Ric Bessin, UK)

Figure 2. A fruit damaged by tomato russet mite and characteristic stem bronzing. (Photo: Ric Bessin, UK)

Problems often begin low on plants and move upward. Russet mite damage can easily be mistaken for disease. These are tiny mites relative to other mites, but can be seen with a 20x hand lens. Incredible numbers of minute mites will develop and cause leaves to turn brown and die. Mites move from these leaves in search of new foliage. Growers often describe  damage as lower leaves being burned or fired-up.  These mites can be blown between plants by fans or carried by workers handling plants.  If russet mite is suspected, growers need to look for them on the upper and lower sides of green foliage just above the damaged leaves. Growers are often surprised how rapidly tomato russet mite problems move through high tunnels. This mite is not in the same family as spider mites, so miticides that just control spider mites may not be effective.

Two-spotted Spider Mite

The two-spotted spider mite is a larger mite when fully mature and usually has a very noticeable dark spot on each side (Figure 3). Body color is variable from yellow to tan to green. They are ‘spider’ mites because they produce a noticeable webbing between plant structures when populations are large. Producers should look for spider mites and the stippling they cause on leaves and fruit (Figure 4).

Figure 3. Two-spotted spider mite is the most common mite species on high tunnel vegetable crops. (Photo: Ric Bessin, UK)

Figure 3. Two-spotted spider mite is the most common mite species on high tunnel vegetable crops. (Photo: Ric Bessin, UK)

Figure 4. Gold flecking of the fruit is common with high spider mite populations. (Photo: Ric Bessin, UK)

Figure 4. Gold flecking of the fruit is common with high spider mite populations. (Photo: Ric Bessin, UK)

 

 Management

These two species are often kept under control in fields through predation by natural enemies.  However, reliance on broad-spectrum insecticides can impact natural enemies and result in damaging populations. In these situations, miticides may be needed, but keep in mind that not all miticides control all mite species. Please refer to High Tunnel & Greenhouse Miticides for information on available miticides.

ducts have restrictions against consecutive applications.; back-to-back applications with the same miticide may foster the development of resistance.  Miticides are not used preventively; they are only applied when mite problems are first noticed. If a second application is needed, a miticide from a different IRAC group needs to be used. Generally, producers should wait a week after a miticide application to assess its effectiveness.

 

By Ric Bessin, Extension Entomologist

 

Posted in Greenhouses/High Tunnels, Vegetables