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A NEW USE FOR METALIZED MULCH FILM IN MANAGING GREENHOUSE PESTS

 

By R. C. Hochmuth, W. L. Laughlin, R. K. Sprenkel, and K. S. Smith

University of Florida/North Florida Research and Education Center

7580 County Road 136, Live Oak , FL 32060-7434

 

 

 

Introduction

The Florida greenhouse vegetable and herb industry represents about 80 acres of intensive production of high quality products. The industry produces a wide variety of crops including tomatoes, cucumbers, peppers, lettuce, strawberries, basil and other herbs.

The industry in Florida generally has a competitive advantage during the winter months due to lower heating costs compared to other areas of the U.S. and Canada. This advantage sets the stage for a market window that requires planting in the early fall, (August – Sept.). This timeframe has high insect populations making pest management perhaps one of the most important production aspects, especially for tomato. The primary tomato pest during the fall is the silverleaf whitefly ( Bemisia argentifolii ). The impact of this pest is magnified by the role it plays in transmitting plant viruses. The viruses transmitted to greenhouse tomato include tomato chlorosis virus, a problem appearing in 1990s and tomato yellow leaf curl virus, a much more serious virus since 2000. In addition, the silverleaf whitefly is responsible for a tomato fruit ripening disorder known as irregular ripening.

The extra challenge in managing insect-vectored viruses in greenhouses is related to the long growing season for the crops. For instance, Florida greenhouse tomatoes are transplanted in September and grown through May or June by keeping the same plants and using cultural practices like leaning and lowering. Once silverleaf whiteflies enter the greenhouse and begin feeding, high levels of virus transmission are likely in Florida even if the whiteflies are killed later. Therefore, insect pest exclusion must be the first strategy in an integrated pest management program for Florida greenhouse growers. Plasticulture products are important to developing a sound insect exclusion plan. Materials such as insect screens have been important for many years, but now metalized plastic mulch may also serve as a new component in an overall insect exclusion plan. Important insect pest exclusion techniques include sanitation, air-lock entrance, resistant cultivars, insect screening, scouting and insect monitoring, reflective or metalized mulches.

Highly reflective or metalized plastic mulches have been used in agriculture for many purposes, but primarily for the repelling effects on certain insects. Metalized mulches are effectively used in field production by covering the narrow raised beds in full-bed polyethylene mulch production system. Research at the University of Florida, North Florida Research and Educational Center in Quincy showed a 30-50% reduction in a thrips-vectored virus, tomato spotted wilt, in field tomato production. Researchers at the University of Florida tested the same approach around the outside of the greenhouses with wide strips of the metalized mulch (Fig 1.) On-farm trials in Suwannee County Florida were conducted in the fall of 2006 to evaluate the effect on reducing whitefly populations from entering the greenhouse.

 

Materials and Methods

An on-farm trial was established at Cheney Farms (Obrien, Florida) in the fall of 2006. Two stand alone side-by-side greenhouses were present at Cheney Farms to conduct the trial. The two greenhouses were similar, but not identical, both approximately 30 x 120 ft, covered with a double layer of polyethylene. Both greenhouses had fan and pad ventilation and both pad areas were covered on the exterior with the same insect screening material.

To evaluate the effectiveness of metalized mulch in the overall pest exclusion program, one greenhouse was used to deploy the mulch (“treated greenhouse”) and the other greenhouse had no mulch deployed (“untreated greenhouse”). The metalized mulch was applied on August 16, 2006 to the ground around the exterior (perimeter) of the treated greenhouse. The mulch was secured to the ground with nursery pins beginning next to the greenhouse structure and covering 10 ft on the sides of the greenhouse and 20 ft in the back of the greenhouse where the evaporative cool pad was located (Fig 1).

The primary pest in the fall season in Florida is the silverleaf whitefly ( Bemisia argentifolii ). Silverleaf whitefly adults were monitored in the trial by using yellow sticky cards inside the greenhouse. Six cards were placed in each greenhouse in the same inside location, two each in the front, center and back of the greenhouse. The total number of adults trapped on the six cards was recorded twice weekly. Cards were replaced or cleaned after each count. Nine whitefly counts were made and recorded from August 22 – September 19, 2006. The greenhouse crops were established by transplanting vegetable and cut flower plants to both greenhouses, although the proportion of the crops was not exactly the same in the two greenhouses.

 

Results and Discussion

The silverleaf whitefly adult populations were always reduced by the use of the metalized much (Table 1). Even before the crops were established on August 22, adult silverleaf whiteflies were found on the sticky cards inside both empty greenhouses. The main reason for entry into the greenhouses was that the adult silverleaf whiteflies were able to get close enough to the evaporative cooling pad and gain entry via the air pulling through the pad. Therefore, the metalized mulch was important in keeping the silverleaf whitefly from getting close to the pad in the treated greenhouse. Over the entire season, the metalized mulch reduced the whitefly adults entering the greenhouse by approximately 90%. The population in the fall of 2006 was extremely high at this location, making it very difficult to totally exclude whitefly from entering the greenhouse. However, the metalized mulch was very effective in further reducing the whitefly populations inside the greenhouse production area.

Several important practices are needed in the implementation of the metalized mulch. The area where the mulch is to be deployed should be prepared by killing vegetation in advance and covering the area with a layer of nursery cloth. The metalized mulch alone over a live grass area is not sufficient to prevent the grass from pushing up the mulch. Standard nursery pins or round top pins can be used to fasten the mulch to the ground. Using clear duct tape or drywall tape in strips on the mulch has been helpful in securing the mulch with the pins. The mulch alone tends to wear a hole around the pin and becomes loose. The contour of the ground should be formed to allow rainwater to run off the metalized mulch. Puddling of water degrades the reflectiveness of the metalized mulch surface.

 

Conclusion

It is important for Florida greenhouse vegetable producers to implement as many IPM exclusion strategies as possible to manage pests. Many of the serious insect pests of greenhouse vegetables, including aphids, silverleaf whiteflies, and western flower thrips, require special control efforts due to their ability to vector plant viruses to the crop. Once these pests enter the greenhouse, growers have very few options to manage them before they transmit virus. Therefore, excluding the pests from entering the greenhouse is critical. Placing metalized mulch around the exterior of the greenhouse can be a very effective strategy in an overall exclusion plan. A virtual tour of the IPM topics covered in this report will soon be added to the Virtual Field Day website of the University of Florida ( http://vfd.ifas.ufl.edu ) as a result of a Florida IPM mini grant.

 

 

 

 

Fig 1 . Metalized mulch application for greenhouse.

 

 

 

 

  Table 1 . Effect of metalized mulch applied to the ground around the exterior perimeter of a greenhouse on the entrance of silverleaf whitefly into the greenhouse (Cheney Farms, Obrien, Florida).

Date	Total number of silverleaf whitefly adults on 6 yellow sticky cards inside the test greenhouse.
	With metalized mulch	No mulch
Aug 22	11	40
Aug 25	16	122
Aug 29	15	43
Sep 01	20	235
Sep 05	18	436
Sep 08	5	96
Sep 12	4	47
Sep 15	2	54
Sep 19	17	146

Note: metalized mulch applied on Aug 16, 2006. Six yellow sticky cards were monitored in each greenhouse and the dates above are the dates the counts were recorded. New cards, or cleaned cards, were placed in the greenhouses after each count.