How to Manage Pests

UC Pest Management Guidelines

Disease symptoms are often difficult to distinguish from nematode, salt, or flooding damage; only a laboratory analysis can provide positive identification.

COMMENTS ON THE DISEASE
Phytophthora species are present in most citrus groves. They can survive adverse conditions as persistent spores in the soil. During moist conditions, large numbers of motile zoospores, which can swim in water for short distances, are produced. Zoospores are the infective agents that are carried in irrigation or rainwater to the roots.

Phytophthora citrophthora is a winter root rot that also causes brown fruit rot and gummosis. Phytophthora citrophthora is active during cool seasons when citrus roots are inactive and their resistance to infection is low. Phytophthora parasitica is active during warm weather when roots are growing.

MANAGEMENT
Management of Phytophthora root rot involves the use of resistant rootstocks, irrigation management, fungicides, and fumigation.

Cultural Control
Provide adequate soil drainage and avoid overirrigating. If destruction of feeder roots is minimal, corrective action may include increasing irrigation intervals, switching to alternate middle row irrigation or a different irrigation system such as minisprinklers, and installing subsoil tiles.

Resistant Rootstocks
When replanting or establishing new plantings, choose resistant rootstocks where possible, but also consider tolerance to other diseases, nematodes, and cold. The most tolerant rootstocks are trifoliate orange, swingle citrumelo, citrange, Alemow, and sour orange.

Organically Acceptable Methods
Cultural controls and the use of resistant rootstocks are acceptable management methods in an organically managed citrus grove.

Monitoring and Treatment Decisions
If a tree growing on susceptible rootstock looks stressed, dig up some soil and check the feeder roots. Sample P. parasitica during July through September, and P. citrophthora during January through March. Phytophthora populations of greater than 15 to 20 propagules per gram of root zone soil may warrant treatment. When planting or replanting in soil infested with Phytophthora, or when susceptible rootstock has to be used, fumigation may be feasible if no other adverse conditions persist.

Common name
(trade name)		Amount to Use
	PREPLANT
A.	METAM SODIUM*	100 gal/acre
		...or...
	(Vapam)	16 fl oz/tree (8 ft diameter canopy)
	COMMENTS: Apply with 6-12 inches of water. Do not plant for at least 45 days.
B.	METHYL BROMIDE*	350-450 lb/acre
		...or...
		8 oz/tree (8 ft diameter canopy)
	COMMENTS: Use low rate on sandy loam and high rate on heavier soils with high clay content. Inject 7-8 inches, 12-18 inches apart, and tarp immediately. Do not plant for at least 1 month.
C.	CHLOROPICRIN*	400-500 lb/acre
		...or...
		16 oz/tree (8 ft diameter canopy)
	COMMENTS: Use low rate on sandy loam and high rate on heavier soils or high clay. Inject 7-9 inches, 12-18 inches apart, and tarp immediately. Do not plant for at least 3 months.
	NONBEARING TREES
A.	MEFENOXAM	1-1.5 fl oz/100 gal water for soil drench
		...or...
	(Ridomil Gold) EC	1-2 qt/acre for soil surface spray
	COMMENTS: For citrus in nurseries: Apply at planting and at 3-month intervals during growing seasons. As a drench, apply 100-250 gal mixture/1000 ft of row on an area wide enough to cover the root system. As a soil surface spray, apply as a broadcast or banded surface spray to seedbeds, liners, or bedded stock in sufficient water to obtain uniform coverage of the root system. For use on resets or new plantings: Apply at planting and up to 3 applications at 3-month intervals to coincide with root growth flushes during the growing season. As a drench, apply 5 gal mix around tree base within the watering ring. As a soil surface spray, apply in sufficient water to obtain coverage of the soil surface wetted by irrigation. Apply spray to the soil surface beneath the tree canopy. Follow immediately with an irrigation sufficient to wet the soil to 1 ft.
B.	FOSETYL-AL	5 lb/100 gal/acre
	(Aliette) 80WDG
	COMMENTS: For use on trees in nurseries only. Apply in 100 gal water/acre to susceptible varieties as a foliar spray when conditions favor the disease. Trees should be treated at time of planting. Spray to wet. Do not exceed 4 applications/year or 20 lb/acre/year.
	BEARING TREES
A.	MEFENOXAM	1-2 qt/acre
		...or...
	(Ridomil Gold) EC	0.75-1.5 fl oz/1000 sq ft
	COMMENTS: Apply 2-3 times/year to coincide with flushes of root growth. Apply in a banded surface spray under tree canopy. Up to 3 applications may be made/year.
B.	MEFENOXAM
	(Ridomil Gold) GR	Label rates
	COMMENTS: Treat in March-April followed by 1 or 2 applications at 3-month intervals to coincide with root flushes; rate depends on tree size and the number of applications/year. Apply 0.5-1 inch water after application.
C.	FOSETYL-AL	5 lb/acre
	(Aliette) 80WDG
	COMMENTS: Apply to susceptible varieties as a foliar spray when conditions favor the disease. Spray to wet. Do not exceed 4 applications or 20 lb/acre/year. Do not apply within 30 days of harvest. Do not allow livestock to graze in treated citrus groves.
*	Permit required from county agricultural commissioner for purchase or use.

PUBLICATION

UC IPM Pest Management Guidelines: Citrus
UC ANR Publication 3441
Diseases
H. D. Ohr, Plant Pathology, UC Riverside
J. A. Menge, Plant Pathology, UC Riverside

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