Citrus weeds

Triazine herbicides have provided a significant contribution to the effective control of weeds in citrus around the world and still are major tools in citrus weed management strategies. 

Day, B.E. (1955). Urea herbicides for citrus weed control. Calif. Citrogr., 40 398, 408-413. 

Giudice, V.L. (1981). Present status of citrus weed control in Italy. Proc. Inti. Soc. Citriculture, 2 486 -87. 

Jordan. L.S., B.E. Day, and D.L. Shaner (1977). Citrus weed control with herbicides. Proc. Inti. Soc. Citric., 487-489. Orlando, FL International Society of Citriculture. 

Tucker, D.P.H. and M. Singh (1983). Florida citrus weed management, J.L. Knapp, ed., Florida Citrus Integrated Pest Management Handbook. Florida Cooperative Extension Service, University of Florida, Gainesville, pp. XII-l-XII-30. 

CgH,3BrN202. A soil-acting herbicide. White crystalline solid, m.p. 158-159" C. It is a non-selective inhibitor of photosynthesis used for weed control In citrus and cane fruit plantations. It is relatively non-toxic to animal life. 

In Hawaii, Faust (2000) contended that the hair sheep, St Croix breed, not only has a unique resistance to parasitic worms but also keeps the coffee, avocado and citrus orchards free of tropical weeds. 

Both lantana and common purslane are weed pests in some crops. Common purslane root exudates inhibited soybean growth but showed stimulation in other bioassays reported in this paper. This may be a concentration and bioassay species dependent effect, since the effect of any toxin varies according to concentration and bloassay species (12). Lantana root exudates showed the strongest inhibitory effect on soybean growth of any of the species tested. Lantana is not found in soybean fields but is a weed pest in some areas in citrus orchards. Holm (13) included lantana, johnsongrass, and cogongrass in his list of the worst weed pests in the world. 

Linares J, Scholberg J, Boote K, Chase CA, Ferguson JJ, McSorley R (2008) Use of the cover crop weed index to evaluate weed suppression by cover crops in organic citrus orchards. Hort Sci 43 27-37... 

The major crops for agrochemical use are cotton, rice, maize, vegetables and top fruit for insecticides small grain cereals, rice, vines and top fruit for fungicides, and maize, soybeans, small grain cereals, rice, industrial weed control, plantations and orchards for herbicides. Other crops that may be of interest include sugar beet, oil-seed rape, potatoes and citrus dependent upon your company s presence in these crops. 

The commercial use of 2,4-D has decreased substantially and (ca 1993) it has general use for home lawns to control broadleaved weeds it also is used on a limited basis to control broadleaved weeds in commercial moncotyledonous crops, eg, sugarcane. 2,4-D is used on citrus when the fruit is 1/3 to 1 inch in diameter to increase fruit size and to limit fruit drop on trees more than six years old. It should not be applied to trees that are in full flush. A further use includes treatment of harvested lemons at 500 mg/L to improve storage properties and to delay yellowing (23). It is used in certain parts of the world to increase latex flow in old mbber tree plantations. 

Although simazine was the first triazine to be developed and marketed in corn as well as other crops, the more versatile atrazine quickly became the standard herbicide in corn. Simazine, however, has remained very valuable and is important on forage crops, ornamentals, turf, and several other vegetable, fruit and nut crops, including almond, apple, artichoke, avocado, berries, cherry, citrus, grape, hazelnut, peach, and walnut. There also remains a strong demand for simazine use in corn in some areas based on specific weed pressure. Simazine is manufactured and sold by several companies today in more than 25 countries around the world, with Brazil, the United States, Australia, and Japan ranked as the top four. 

In 2004, terbuthylazine continues to be a major component of herbicide programs in Europe, especially in com. At a country level, the Netherlands treats almost 100% of com, while on the low end, Austria treats 35% of com hectares with terbuthylazine. Approximately 60% of the combined area in corn production in Europe received terbuthylazine, including Germany, Italy, and Belgium. Terbuthylazine is used in more than 45 countries and remains a key weed control tool in crops such as com, sorghum, pea, bean, lupin, grape, pome fruit, citrus, and vine. 

Benefits of Triazine Herbicides and Other Weed Control Technology in Citrus Management... 

Simazine was among the first herbicides registered for use in Florida citrus in 1962 and was recommended by the University of Florida as an excellent weed control tool for citrus (Kretchman and McCown, 1962). This early registration of simazine was for the control of annual weeds, while today s registration includes broadleaf weeds, annual vines, and annual grasses (Singh and Tucker, 1987). 

This chapter will deal with citrus losses caused by weeds, major weeds infesting citrus groves around the globe, and controlling weeds in citrus with a special emphasis on triazine herbicides. A brief description of the control measures available in different parts of the world and their limitations are discussed. 

California trees, citrus tree trunk and canopy growth, leaf nitrogen level, fruit yield, and fruit quality were decreased by competition from annual weeds and bermudagrass (Jordan, 1981). Suzuki (1981) reported that in Japan, weeds in summer absorb and transpire large amounts of water from the soil and compete with citrus trees. Moisture and nitrogen levels in the soil decreased particularly where large crabgrass and tufted knotweed were present (Ito and Ukei, 1981). 

Major Weeds of Citrus and Their Economic Impact... 

Citrus trees are a long-term investment, and growers cannot afford crop damage or yield loss from weed competition, cultural operations, or misapplication of chemicals. The most critical time to control weeds in trees is from planting to early establishment, which spans from 3 to 6 years depending upon soil fertility. 

Slashing, Hand Hoeing, and Mulching Bredell (1973) compared several physical methods with chemical measures to control weeds in citrus. Herbicides were found to be the most effective tool in managing weeds. Depending... 

Weed Control with Hot Water Hot water to control weeds in citrus orchards and in other crops has shown potential (Anonymous, 1993a, b). The results of such treatments were comparable to contact herbicides. 

Cover Crops Ideal cover crops should suppress weeds and provide little interference with the citrus crop. Jones and Embleton (1967) recommended using legumes in young citrus orchards before weeds become thoroughly established. However, in mature orchards, other alternatives such as mustard species are used as cover crops in citrus orchards. 

Insects This method has received little attention as a means of combating weeds in citrus. Habeck (1977) showed that insects could be used against largeleaf lantana and stranglervine. A number of leaf-mining beetles have been used successfully in Australia and Hawaii to control largeleaf lantana, which is a major weed in Florida citrus orchards (Tucker and Singh, 1983). 

Chemical weed control practices in citrus have been thoroughly reviewed by various researchers (Ryan, 1969 Jordan et al, 1977 Jordan, 1978 Tucker and Singh, 1983 Mersie and Singh, 1989 Singh el al., 1990 Sharma and Singh, 1999). Herbicides used in citrus can be divided into two groups soil-applied (preemergence) and... 

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