How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS AND SIGNS

Symptoms include yellow orange pustules oriented linearly between vascular bundles of leaves. Glumes are often infected. Stripe rust symptoms usually appear earlier in the season than other rusts because the fungus develops at lower temperatures than the other rust fungi. As the plants mature, the pustules turn dark and shiny as teliospores are formed. These spores do not play a role in disease development or survival.

COMMENTS ON THE DISEASE

Different races (strains) of the stripe rust pathogen affect wheat and barley. The stripe rust fungus has been responsible for some of the most devastating epidemics on wheat in California.

Races that can cause significant damage to barley were confined to Europe until 1975, when they were introduced into South America. Barley stripe rust was first detected in the U.S. in Texas in 1991 and in California in 1993/94. Major epidemics on barley in California occurred in 1996, 1997, and 1998.

The fungus grows only on living host plants and survives between seasons on volunteer wheat, barley plants, and some wild grasses. Rust spores are spread by wind to initiate infections. Disease development is most rapid at temperatures of 50° to 60°F (10° to 16°C) with intermittent rain and dew, although disease can continue to develop at higher temperatures and drier conditions; secondary cycles occur at 7- to 10-day intervals. Races infecting barley can survive in warmer, drier climates. Infections increase water loss and decrease the amount of photosynthate available for grain filling, resulting in reductions in the number and weight of kernels.

MANAGEMENT

Control is achieved through the use of resistant cultivars (see BARLEY and WHEAT CULTIVAR TABLES). A statewide monitoring program exists for early detection of susceptible genotypes and identification of new resistant genotypes.

Chemical Control
In the event that new races of the fungus render current sources of resistance obsolete, foliar fungicides can be applied to control disease outbreaks. Application timing will depend on when initial infections occur and on the specific label restrictions for each fungicide; the objective is to protect the flag leaf from infection and to protect the plant during the grain-fill period.

Common name		Amount/Acre**	R.E.I.+	P.H.I.+
(trade name)			(hours)	(days)
The following materials are listed in order of usefulness in an IPM Program, taking into account efficacy. Also consider the general properties of the fungicide as well as information relating to environmental impact. Not all registered pesticides are listed. Always read label of product being used.
A.	PROPICONAZOLE
	(Tilt)	2–4 fl oz	24	0
	MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
	COMMENTS: For wheat, apply until Feekes growth stage 10.5 (full head emergence). For barley, apply until Feekes 9 growth stage (emergence of flag leaf ligule). For both crops do not exceed 4 fl oz/acre/season.
B.	AZOXYSTROBIN
	(Quadris)	6.2–10.8 fl oz	4	45
	MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
	COMMENTS: For use on barley and wheat. Do not apply after heading is completed (Feekes 10.5). Do not make more than 2 applications/season.
C.	PYRACLOSTROBIN
	(Headline)	9 fl oz	12	see comments
	MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
	COMMENTS: For use on barley, rye, triticale, and wheat. Do not apply to barley after 50% head emergence (Feekes 10.3) or to wheat after heading is completed (Feekes 10.5). Do not harvest wheat or barley hay or feed green-chopped wheat or barley within 14 days of last application. Do not make more than 2 applications/season.
D.	TRIFLOXYSTROBIN/PROPICONAZOLE
	(Stratego)	see comments	24	see comments
	MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) and Demethylation inhibitor (3)
	COMMENTS: On wheat: rate is 10 fl oz/acre. Do not apply after Feekes growth stage 10.5 (full head emergence). Do not make more than 2 applications/season or apply within 35 days of harvest. If one application or a total of 10 fl oz of Stratego per season is applied, do not allow livestock to graze within the treated area within 30 days after application, and do not harvest the treated crop for forage within 30 days after application or use for hay within 45 days after application. If 2 applications or a total of 20 fl oz of Stratego per season is applied, do not allow livestock to graze within the treated area and do not harvest the treated crop for forage or hay. On barley: rate is 7 fl oz/acre. Do not apply after Feekes growth stage 8 (emergence of flag leaf ligule). Do not make more than 2 applications/season or apply within 40 days of harvest. If 1 application or a total of 7 fl oz is applied per season, do not allow livestock to graze within the treated areas within 30 days after application, and do not harvest the treated crop for forage within 30 days after applications or for hay within 45 days after application. If two applications or a total of 14 fl oz is applied in a season, do not allow livestock to graze within the treated area and do not harvest the treated crop for forage or hay.
+	Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
**	See label for dilution rates.
1	Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of actions (for more information, see http://www.frac.info/). Fungicides with a different group number are suitable to alternate in a resistance management program. In California, make no more than one application of fungicides with mode of action Group numbers 1, 4, 9, 11, or 17 before rotating to a fungicide with a different mode of action Group number; for fungicides with other Group numbers, make no more than two consecutive applications before rotating to fungicide with a different mode of action Group number.

PUBLICATION

UC IPM Pest Management Guidelines: Small Grains
UC ANR Publication 3466
Diseases
R. M. Davis, Plant Pathology, UC Davis
L. F. Jackson, Agronomy, UC Davis

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