A survey of weeds and herbicides in Georgia Pecan

Authors: GREY, TIMOTHY - University Of Georgia; TURPIN II, FRED - University Of Georgia; WELLS, LENNY - University Of Georgia; Webster, Theodore

Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2014
Publication Date: 7/1/2014
Citation: Grey, T.L., Turpin Ii, F.S., Wells, L., Webster, T.M. 2014. A survey of weeds and herbicides in Georgia Pecan . Weed Technology. 28:552-559.

Interpretive Summary: Pecan production is increasing in the United States as exports to foreign markets have stimulated pecan value and spurred newly planted orchards. In the US, Georgia ranks number one in pecan production accounting for 46,266,000 kg of production on 60,300 ha with value of $265,000,000. Over 3,240 ha of pecan trees seedlings were planted in 2012 in Georgia. However, there is limited weed control information and herbicide usage data with respect to grower practices. There were 44 Georgia counties represented and 200 participants for the survey of troublesome weeds and herbicide use practices. Wild radish was the most troublesome weed problem that occurred in Georgia pecan orchards occurring as a winter species in tree rows and vegetative areas between tree paths. Additionally, 34% of growers stated that wild radish was the most difficult weed to control in the orchard and reported as a problem in 67% of newly planted (<5 year olds) and established orchards. Italian ryegrass was the second most troublesome winter weed in pecan orchards. Curly dock was the only winter perennial weed species on the list that was considered problematic by growers. Amaranthus species, including Palmer amaranth, were the most troublesome summer annual weed species in Georgia pecan orchards. In the GA Pesticide Handbook recommendations for pecan weed control, there are herbicides that represent 10 different mechanisms of action. Survey results determined that PRE herbicides were applied by 67% of the growers. The survey indicated that pecan growers are applying different mechanisms of action at various times of the calendar year, which is critical in preventing weed shifts and establishment of herbicide resistance populations. However, many pecan growers are focused on using too few herbicide products relying on POST only applications. There needs to be greater use of the various mechanisms of herbicide actions available in order to prevent resistance from becoming a further problem. If growers would adapt greater PRE herbicides, then fewer POST applications would be required to manage weeds in pecan orchards. In return, this can reduce the number of required herbicide applications reducing labor and fuel costs. These management programs need to have PRE herbicides applied in the spring and autumn, and POST herbicides when weeds are below 10 cm in size for optimum control. By adapting PRE and POST management systems, cost of labor and fuel could decrease due to fewer applications. Increasing the number of mechanisms of action to avoid resistant biotypes will also assist in weed management. Given that pecan weed management is a year round battle, the herbicides utilized need to be alternated in order to prevent over use in any given year. Thus, some problematic weeds that are occurring in Georgia could be avoided.

Technical Abstract: A survey was conducted in 2012 in Georgia to determine the most troublesome weeds in pecan orchards and document common weed control practices using herbicides. Weed control practices and infestations in pecan were divided between winter and summer seasons. The most troublesome pecan winter weed species were wild radish and Italian ryegrass, with the most troublesome summer weed being Palmer amaranth and bermudagrass. Other weeds included crabgrass, bahiagrass, Florida pusley, purslane species, morningglory species, curly dock, and cutleaf eveningprimrose. The most widely used POST herbicide was glyphosate applied in both winter and summer seasons. The most commonly used year-round herbicides with soil persistence were pendimethalin, diuron, flumioxazin, halosulfuron, simazine, indaziflam, and oryzalin. Use of multiple herbicides; both PRE and POST contact and soil persistent, with various herbicides mechanisms of action has benefited pecan producers by providing year-round weed control, even with herbicide resistant weeds being widely established in this region.