Botryosphaeria Panicle and Shoot Blight

Vegetative and flowering buds that were killed during the previous fall or winter do not emerge in spring. In mid-spring (end of May to June) buds that were partially infected the previous season produce fruit clusters and shoots that develop blight from the fungus in buds. The rachises of these blighted clusters turn black as do the shoots. When temperatures increase in May through July, the fungus moves into shoots of the previous year, causing blighting of fully developed clusters. These blighted shoots, leaves, and clusters turn brown.

Secondary infections of clusters originate where the rachises branch; they start as small black lesions that later coalesce and cause fruit blight. Secondary infections of fruit start as round, black, pin-sized lesions, some of which will expand and decay the hulls. In late August through September, infected fruit are covered with pycnidia (black flasklike structures containing the fungus spores of the Neofusicoccum sp.) and obtain a silvery color, in contrast to the noninvaded blighted fruit, which are brown.

Infections on leaves also start as small black lesions that later coalesce and cause leaf blight. From August through October, large necrotic lesions with pycnidia in the center develop on leaves of male and female trees. Infection of petioles start as longitudinal black areas and cause blight of the entire leaf or of individual leaflets and defoliation. Scars of abscised buds or leaves can also be infected, resulting in sunken cankers above and below the scars. Infected rachises usually hang on the tree for 3 to 4 years, providing inoculum for the following growing season(s). On branches, lenticels can also be infected, but the infections remain small and do not invade the shoot.

To distinguish from Alternaria spp., rub leaf lesions with a finger

• If finger blackens the lesion is caused by Alternaria spp.
• If finger does not blacken the lesion is caused by Botryosphaeria dothidea (no spores are produced on the surface of these lesions.

However, late in the season both fungi can be present in the same lesion and microscopic identification will be needed.

Sources of inoculum for this disease are rachises, shoots, and petioles killed during the previous growing season that remain on the trees. Cankers can also provide inoculum for as long as 6 years. Spores from these sources cause primary infections on the vegetative and flowering buds. Secondary infections subsequently occur on shoots, rachises, fruit, and leaves from spores produced in the primary infected plant parts. The pathogen can cause latent infections on buds, leaves, and fruit. Symptoms of the disease are triggered to develop by temperatures over 86°F (30°C).

Spores are spread in water from spring and summer rains, via water from sprinkler irrigation, or other means (birds, hemipteran insects, etc.). The optimum temperature range for disease development is 80° to 86°F, and the disease can become very severe during late spring to summer when temperatures and relative humidity in pistachio orchards are high.

Botryosphaeria panicle and shoot blight is extremely difficult to control, especially if allowed to increase over several years. The best approach employs monitoring, pruning, fungicides, and irrigation management.

To reduce disease incidence, lower sprinklers to prevent water from reaching the tree canopy or shorten the duration of irrigation from 48 to 24 hours. You may irrigate only during the daytime for 12 hours in 2 consecutive days to significantly reduce disease.

When disease incidence is low, pruning blighted shoots and panicles, shoots with cankers, dead and dying wood, and removing infected wood from the orchard can help reduce or eliminate inoculum for a few years. During late summer, after harvest, and during dormancy prune out infected areas 2 inches past blighted margins.

After harvest remove and destroy unharvested nuts and mummies to reduce sources of inoculum. At minimum shake trees and remove mummies as soon as possible before rain. Mummy removal will also reduce navel orangeworm.

Organic growers need to emphasize careful pruning to remove as much infected plant tissue as possible. Applying the fungicide Regalia is an organically acceptable method.

Monitoring

During dormant and delayed dormant pruning activities, look for Botryosphaeria cankers noting trees of concern. Continue to look for shoot strikes two to three times during the growing season.

Predictive Tests

Two tests are available that predict disease risk at harvest. A preseason bud-monitoring test (BUDMON) detects bud infection incidence and predicts risk for panicle and shoot blight at harvest. A growing-season test (ONFIT = overnight freezing-incubation technique) of immature fruit provides treatment thresholds. For information on diagnostic labs that perform these tests ask your local farm advisor or pest control adviser.

Management

If your orchard has a severe history of Botryosphaeria panicle and shoot blight or you find cankers, plan to apply a fungicide when panicles appear in spring. When the disease is severe, both pruning and fungicide treatment are suggested.

Apply two to three applications of QoI strobilurins (azoxystrobin, pyraclostrobin, or trifloxystrobin) starting at bloom. Pyrimethanil (Scala) is only effective when the disease is low to moderate in severity.

Time your fungicide applications before a rain event (if missed, an application can be applied 2 to 3 days after rain occurs); it has been shown that applications before or after rain reduce the number of calendar sprays.

Also consider the results of BUDMON or ONFIT tests to decide whether additional sprays are necessary.

	Sampling	Risk Results (% infected plant part)
BUDMON	Between February and mid-March randomly collect 100 flower or vegetative buds from each quadrant of the orchard, placing them in a paper or plastic bag and bringing them to a lab.	0%: no disease expected 1–3%: low levels of disease 4–8%: moderate levels of disease =9%: high levels of disease expected Consider treating when results show moderate to high risk.
ONFIT	In mid June to early July (the latest), randomly collect 100 immature fruit from each quadrant of the orchard, placing them in a paper or plastic bag in an ice chest, and bringing to a lab.	0%: no additional treatment is needed 1–3%: one fungicide application (treat last week June or first week July) >5%: two fungicide applications may be needed (treat last week June or first week July; repeat 2 to 3 weeks later)

	Common name	Amount per acre	REI‡	PHI‡
	(Example trade name)		(hours)	(days)
Pesticide precautions Protect water Calculate VOCs Protect bees
Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least likely to cause resistance are at the top of the table. When choosing a pesticide, consider information relating to the pesticide's properties and timing, honey bees, and environmental impact. Always read the label of the product being used.
A.	FLUOPYRAM + TEBUCONAZOLE
	(Luna Experience)	6–8 fl oz	12	35
	MODE-OF-ACTION GROUP NAME (NUMBER1): Succinate dehydrogenase inhibitor (7) and demethylation inhibitor (3).
B.	FLUOPYRAM + TRIFLOXYSTROBIN
	(Luna Sensation)	5–7.6 oz	12	28
	MODE-OF-ACTION GROUP NAME (NUMBER1): Succinate dehydrogenase inhibitor (7) and quinone outside inhibitor (11)
C.	POLYOXIN-D ZINC SALT
	(Ph-D)	6.2 oz	4	0
	MODE-OF-ACTION GROUP NAME (NUMBER1): Chitin synthesis inhibitor (19)
D.	AZOXYSTROBIN + PROPICONAZOLE
	(Quilt Xcel)	12.5–21 oz	12	60
	MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3) and quinone outside inhibitor (11)
E.	AZOXYSTROBIN + DIFENOCONAZOLE
	(Quadris Top)	12–14 oz	12	14
	MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3) and quinone outside inhibitor (11)
F.	TEBUCONAZOLE
	(Tebuzol 45DF)	8 oz.	12	35
	MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
G.	PYRACLOSTROBIN + BOSCALID
	(Pristine)	10.5–14.5 oz	12	14
	MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) and carboxamide (7)
H.	TRIFLOXYSTROBIN
	(Gem 500SC)	1.9–3.8 fl oz	12	28
	MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
	COMMENTS: Apply at 2- to 3-week intervals beginning at late May to early June. Do not apply more than 4 times per season.
I.	AZOXYSTROBIN
	(Abound 2EC)	12.3–15 fl oz	4	7
	MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
	COMMENTS: Apply at 2- to 3-week intervals beginning late May to early June. Do not apply more than 4 times per season.
J.	PYRACLOSTROBIN
	(Cabrio EG)	16 oz	12	14
	MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
	COMMENTS: Apply before disease onset and repeat at a 10- to 30-day interval.
K	PYRIMETHANIL
	(Scala SC)	18 fl oz	12	30
	MODE-OF-ACTION GROUP NAME (NUMBER1): Anilinopyrimidine (9)
	COMMENTS: Use under low and moderate disease pressure.
L.	THIOPHANATE-METHYL
	(Topsin M WSB)	1.5–2 lb	72 (3 days)	—
	MODE-OF-ACTION GROUP NAME (NUMBER1): Methyl benzimidazole (1)
	COMMENTS: Apply at bloom.
M.	CYPRODINIL + FLUDIOXONIL
	(Switch 62.5WG)	11–14 oz	12	7
	MODE-OF-ACTION GROUP NAME (NUMBER1): Anilinopyrimidine (9) and phenylpyrrole (12)
	COMMENTS: Make first application at early bloom and a second 14 days later.
N.	REYNOUTRIA SACHALINENSIS EXTRACT#
	(Regalia)	Ground application: 1–4 qt	4	0
	MODE-OF-ACTION GROUP NAME (NUMBER1): Plant extract (P5)

‡	Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) 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.
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.
—	Not applicable.