V e g e t a r i a n  N e w s l e t t e r
UF/IFAS - Horticultural Sciences Department A Vegetable Crops Extension Publication
  VEgetarian 04-02 February 2004 Print Version

February is Potato-planting Season for Home Gardeners in North and North-central Florida

Figure 1. Standby varieties that can normally be found in farm and garden supply stores.

Figure 3. Cut seed pieces at least one good “eye."

(Jacque Breman, Union County Extension Director - Vegetarian 04-02)

Intelligent Pest Management Practices Started the Strawberry Season

What a year! From our perspective, 2003 will be one of the most memorable for the strawberry industry (although we still have three months to go until the end of the season!). According to Al Herndon (Ferris Farm, Floral City), “This season has been outstanding as compared with the 2002-2003 season” (Fig. 1). Just to remind you, the low temperatures in the months of January and February 2003 challenged Florida fruit and vegetable production. Nevertheless, by February 2004 the strawberry harvest has been well under way. Some folks had already experienced early problems with twospotted spider mite, aphids, and budworms; however, proper decisions and good timing made control measures effective in most cases.

summary of the season

Dr. Jim Price, UF Gulf Coast Research and Education Center (GCREC), indicated that this year, strawberry transplants arrived with less than usual spider mites than previous years.  Some growers reported better than expected results for spider mite clean-up of young transplants by applying Brigade (bifenthrin) pyrethroid plus diazinon (organophosphate) after the transplant establishment period (Fig. 2).  Dr. Price added that we should not expect serious losses from spider mites even with an expected increase in mite numbers in February since several effective biological and chemical control measures are now available. Appearances of other pests such as Lepidopterous larvae (‘worms’) and aphids normally occur in February and thereafter since good control measures are available for these pests. Price indicated that thrip problems increase in warm weather, which continued this season into early January 2004. However, since colder days arrived there seems to be no current increase in thrip numbers. According to Hillsborough county agent, Alicia Whidden (Berry/Vegetables Times January 2004), some farmers reported fruit bronzing and cracks under the calyx. These problems were due to consecutive applications of sulphur for powdery mildew as well as thrip and aphid damage. UF researchers are investigating the sulphur related damage in order to minimize the ill effects of the fungicides.

Biological Control of Twospotted Spider Mite

For the past couple of years, we have studied the impact of biological control methods for strawberry arthropod pests. For instance, in an effort to increase the effectiveness of predator mites as a control of twospotted spider mites (Fig. 3), we have set up three experimental trials in Floral City (Citrus County), Plant City (Hillsborough County), and Dover (Hillsborough County) to evaluate the feasibility of using two predatory mites: Phytoseiulus persimilis Athias-Henriot and Neoseiulus californicus  McGregor. This project collaborates with growers, extension agents, and crop consultants to conduct on-farm demonstrations and experiment station trials. The project will also determine the potential for using predatory mites in combination with reduced-risk pesticides to control twospotted spider mites. Information obtained from these studies will be presented in workshops and field-days this spring and summer to train growers in basic biological control pest management techniques.

Benefits of Using an Intelligent Management Approach

Some of the pesticides that are currently used on Florida strawberry farms to control arthropods and diseases include organophosphates which are considered to pose the greatest risk for human health and the environment. The high level of pesticide use combined with the method of frequency of harvesting means that there is a risk of occupational exposure to these pesticides by crop workers. Reduction of pest control usage in strawberries through Intelligent Best Management practices based on various control measures (cultural, biological, and chemical control compatible with biological methods) are important to follow to reduce environmental hazards and human exposure, cost, and insect resistance. Thus, the continued use of only one practice, i.e. chemical control only, can be extremely costly in terms of not only costs for the chemicals and applications but more importantly  losses due to rapid build-up of chemical resistance to the applied chemicals. Ultimately, the combination of control measures leads to the greatest returns to profit in terms of fruit quality and yield for the least ‘long term’ expense.

Fig. 1. Field strawberry production under way. Healthy young strawberry plants in raised beds and plastic mulch.

Fig. 2. Population dynamics of twospotted spider mite after Brigade plus Diazinon application. Only one insecticide application was made 10/21/03. Percentage of twospotted spider mites steadily decreased throughout the season (y axis by 10).  (Click here for larger image of Fig. 2)

Fig. 3. A Twospotted spider mites on a strawberry leaf.

If you have any questions regarding this article, please contact Drs. Silvia I. Rondon (srondon@ifas.ufl.edu) and Daniel J. Cantliffe (djc@ifas.ufl.edu). For more information, visit http://www.hos.ufl.edu/ProtectedAg/.

(Silvia Rondon, adjunct research associate, and Cantliffe - Vegetarian 04-02)

Rotational Crop Restrictions

In the past, there have been some questions raised about whether the rotational crop restrictions on a herbicide label are simply for the protection of the manufacturer, in case rotational crops are damaged, and to supply information to the grower about potential crop injury.  In fact, the rotational restrictions are fully enforceable. 

Barry Brecke, West Florida REC - Jay, sent out a letter documenting the background of cotton injury a year after Cadre application in peanuts.  A DOACS inspector was called to a grower field in the panhandle during the summer 2003 to look at damaged cotton.  The inspector discovered that they had applied Cadre to peanuts grown in the field during 2002. The inspector told the grower that he was in violation of the Cadre label (which lists the minimum time between Cadre application and cotton planting as 18 months) and wrote the grower a warning letter concerning this “violation” of the Cadre label.  The same inspector during a routine check of spray records of another grower discovered that the second grower had also planted cotton in a field in 2003 where peanuts had been grown and treated with Cadre in 2002.  In addition, the records of the second grower indicated that the surfactant used with the Cadre contained 70% active ingredient while the Cadre label states that the surfactant with at least 80% active ingredient is to be added to a Cadre application.  The inspector included the surfactant “misuse” in the warning letter to the second grower.

Dr. Brecke checked with Dale Doubberly, DOACS Enforcement, and he assured him that the rotational restrictions are an enforceable part of the label. Greg MacDonald also checked with Carlton Lane who is recently retired from US EPA. The following is his response:

Yes the directions are fully enforceable.  Anything on the label that is an affirmative instruction - do or do not - is enforceable even though the grower may have suffered harm as a result of the error or intentional “mistake”.  There is no such thing under the law as no harm, no foul.  An agency might take the harm under consideration and mitigate the penalty, but private applicators who are caught in the practice you describe are simply giving up their free pass.  The next time they are caught, it will result in a fine on top of their damage.

Vegetable growers are going to have to become more informed on rotational restrictions of the herbicides used and what crops can follow, especially with methyl bromide alternative options under mulch.  There still are rotational crops restricted for a period of time even though there are now tolerances and labels of the herbicide or another herbicide with the same active ingredient on that crop.  We are working with the companies to reduce or eliminate these problems.  If anyone has specific plant-back restriction information that should be brought up with registering companies, please let us know.

 (Stall- Vegetarian 04-02)