Use of Mulches to Manage Aphids Vectoring Cucumber Mosaic Virus
Joe Nunez, UCCE, 1031 South Mount Vernon Ave., Bakersfield California 93307
We have been working on a project looking into ways to repel aphids and thrips from pepper plants to prevent virus infection has been carried on since 2008 in Kern. The trial has been conducted in a growerís field in an area of the county that often has cucumber mosaic virus (CMV) of peppers.
Silver reflective mulch has been used as a method to repel aphids and thrips from various crops to prevent virus transmission. It is often used on tomatoes, melons, and peppers to prevent virus infection such as tomato spotted wilt virus (TSWV), tobacco mosaic virus (TMV), CMV and others. Other colored plastic mulches have been shown to increase plant size and yield. Probably the main use of plastic mulch on vegetables here in California however is for weed control. Black colored plastic mulch does an excellent job of shading the soil surface thus preventing weed growth. Sometimes clear plastic mulch is used to warm the bed for early season planting in the spring.
The main objective of this study was to determine which plastics mulches besides silver reflective mulch could repel aphids and thrips to prevent virus transmission. Another objective was to determine if a more cost effective spray on mulch could be used to repel aphids and thrips. Lastly determine what effect these different mulches have on plant growth and yield.
The treatments used in 2010 were
- control-bare soil
- black mulch
- silver reflective mulch
- silver mulch (more like a grey color in reality)
- white mulch
- green mulch
- red mulch
- kaolin clay sprayed on canopy
- kaolin clay sprayed on soil surface
The plastic mulches were applied with a mulch layer onto 60 inch beds. After applying the mulch, the plots were planted on 3/24/10 with bell pepper transplants, two rows per bed. The kaolin clay was sprayed after transplanting either onto the canopy or onto the bed on each shoulder and in between the two transplant rows. The kaolin clay was sprayed as needed as the plant canopy grew and after spring rains which tended to wash the kaolin clay off. Surround by NovaSource was the source of the kaolin clay. Each individual plot was fifty feet in length by one row and replicated four times.
Aphids and thrips were monitored on a weekly basis by the use of yellow sticky cards that were placed a few inches above the canopy. At harvest twelve plants per plot were hand harvested of all commercially acceptable sized fruit and weighed.
During the course of the growing season obvious differences in growth could be seen between the various colored mulches. To confirm this four plants per plot were sampled and weighed for biomass production at week eight after planting. The plants were divided into roots and top and weighed for fresh weight and dry weight. The black, silver, red and green plastic mulch had significantly greater plant mass than the bare soil control (table 1). All other treatments were the same as the bare soil control.
Aphid counts were minimal the first week but increased considerably by week two and three before going down again to lower numbers. On week 2 all the treatments had less aphid counts than the bare soil control. At week three all but the white plastic mulch had significantly less aphid activity than the bare soil control. This trend continued on week four but after that the aphid counts dropped to very low counts for the rest of the season. Total aphid counts trapped over the entire 10 week period showed all the treatments were significantly better than the bare soil control. The best treatments were the silver reflective and silver mulches with the red, green and kaolin clay applied on the soil surface close behind.
Thrip counts were significant after the first week and stayed high during the course of the season. The silver reflective and silver mulch along with the kaolin clay sprayed on the canopy had significantly less thrips than the control. The white colored mulch actually increased the number of thrips by a significant amount. All other treatments were statistically the same as the bare soil control.
For harvest data twelve plants per plot were stripped of all fruit that was of commercial size. The fruit were then placed into size categories of jumbo, large, medium and small. These were subdivided into market or process types. Market fruits are nearly perfect in shape and likely be sold for fresh market. Process types are slightly misshapen and likely would be sold to be processed and frozen. There were essentially no differences in yields among all the treatments. There was a slight difference in the market medium with the silver reflective mulch having less fruit to all other treatments.
The black, red and green plastic mulches increased the size of the plants. This growth difference was easily visible during the entire season. All of the treatments reduced aphid flights onto the plots as compared to bare soil control. Thrips were reduced by the use of silver reflective and silver mulch along with the kaolin clay sprayed on the canopy.
There was no difference in fruit yield even though we saw significant differences in aphids and thrip counts plus growth differences all due to the various treatments we applied. It is important to note that cucumber mosaic virus was not a factor in 2010 even though aphid activity was present.
If CMV was present then differences in yield would most likely be related to the aphid counts. In 2008 we saw significant aphid activity and CMV presence. In that trial yields were increased due to less CMV which was a result of less aphid flights by the silver reflective mulch. In 2009 we did not have much aphid activity or CMV but saw that the red, green and black color mulches did significantly increase yields.
After three years of trialing some conclusions can be made. First, any colored plastic mulch or kaolin clay spray can significantly reduce aphid flights onto plants. Secondly, the amount of virus that may appear in a crop can be reduced significantly by reducing aphid flights onto that crop. And lastly, black, red and green plastic mulch will have a positive impact on plant growth and vigor which may result in increased marketable yields of peppers.
Table 1. Dry weights of plants 8 weeks after transplanting
|Dry Wt (g) ___ 5/21/10|
|Treatment||Top Wt.||Root Wt.||Total|
|3. Silver Reflective||49.4||d||6.8||c||56.1||d|
|8. Surround Canopy||47.8||d||8.0||a||b||c||55.8||d|
|9. Surround Soil||54.9||c||d||6.9||c||61.8||c||d|
Table 2. Total aphids and thrips trapped during season.
|Total Aphids and Thrips|
|3. Silver Reflective||30.6||d||4687.2||c||d||e|
|8. Surround Canopy||74.4||b||3923.0||e|
|9. Surround Soil||46.3||c||d||5657.8||b||c|
Table 3. Total harvest weights of peppers.
|3. Silver Reflective||5.5||c||3.5||9.0|
|8. Surround Canopy||5.6||c||3.6||9.2|
|9. Surround Soil||6.9||a||b||c||3.4||10.3|