Anthracnose management in peppers – the old and the new

By: Katie Goldenhar and Amanda Tracey

Anthracnose in Ontario field peppers has been historically caused by the fungal pathogens Colletotrichum coccodes and C. dematium. These are endemic to Ontario and mainly infect ripe fruit. The disease has typically been controllable through use of fungicides applied on a 14-day interval starting after fruit set. In 2020, a severe anthracnose outbreak occurred in one processing pepper field. Samples were taken from the field, sent for diagnosis and subsequently identified as Colletotrichum scovillei, a new species to Ontario. In 2021, anthracnose in peppers was seen in late July in multiple pepper fields. The disease spread quickly and was extremely aggressive with more than 80% of fruit (immature and mature) infected with at least one lesion by late August.

Colletotrichum scovillei has been reported in South Carolina, Brazil, China, Indonesia, Japan, Malaysia, South Korea, Taiwan and Thailand. Colletotrichum scovillei is part of the C. acutatum species complex, which can cause symptoms on immature fruit. Colletotrichum scovillei hosts are primarily within the Capsicum (pepper) family.

Biology and Spread

Colletotrichum species may overwinter on infected pepper fruit left in the field or on infected plant material at the end of the production season. Additionally, if crop debris remains on equipment, this may serve as an overwintering source for the disease. Pepper anthracnose usually starts out as a ‘hot spot’ in the field and then fans out directionally with the prevailing wind and driving rain. The spores of Colletotrichum species are spread through splashing water, rain or irrigation, driving winds and equipment/people. Hot weather along with afternoon and evening showers are ideal conditions for anthracnose development.

Symptoms

Colletotrichum species are known to have latent infection periods, where they infect flowers or developing fruit and do not show symptoms until weeks after. Colletotrichum scovillei can cause lesions on small, immature fruit as well as mature fruit. Samples of asymptomatic fruit were collected and fruit without any visible lesions (between 1-5 cm) were found to already be infected. Infected fruit can have one or more soft, sunken lesions covered with salmon-colored spore masses (Figure 1).

Management

Cultural controls for anthracnose should include starting with clean transplants. Scout regularly and remove infected plants, including plants surrounding the diseased one as soon as symptoms are seen. Rotating away from peppers, ideally a 3-year rotation or more, can help reduce inoculum pressure. Avoiding the use of overhead irrigation can help reduce the leaf wetness period needed for infection. Remaining plant debris should be mulched/mowed and then incorporated into the soil as soon as harvest is finished to allow for the soil microorganisms to break down the residue. Clean and disinfect equipment including irrigation hoses, baskets, tractors, trucks, wagons, etc. before storage.

Fungicide applications targeting anthracnose should start at flowering and continue on a 7-to-10-day interval until harvest. Make sure the sprayer is well calibrated and the fruit is receiving adequate coverage. Table 1 outlines the fungicides registered in Canada for pepper anthracnose. Group 11 fungicides (Cabrio and Quadris Top) are heavily relied on for anthracnose control. When using group 11 (QoI) fungicides, the Fungicide Resistance Action Committee (FRAC) recommends that in programs in which applications of QoI are made with both solo products and mixtures, the number of QoI containing applications should be no more than 50% of the total number of fungicides applied per season. Table 2 gives an example of a spray program for C. scovellei including the new Emergency Use Label for captan. A spray program beginning at flowering could have 10 or more fungicide applications.

Table 1. Fungicides registered on field peppers for the 2022 field season for anthracnose. Note that captan is an Emergency Use Label for one year.

Active ingredient	Product	FRAC Group	Maximum # of applications per year	Pre-Harvest Interval (days)
copper sulphate	Copper 53W	M1	10	2
captan	Catan 80 WSP	M4	3	3
pyraclostrobin	Cabrio	11	6	0
azoxystrobin/ difenoconazole	Quadris Top	11 & 3	3*	1
difenoconazole/ benzovindiflupyr	Aprovia Top	3 & 7	4*	1
difenoconazole/ pydiflumetofen	Miravis Duo	3 & 7	2*	0
fludioxinil/cyprodinil	Switch	12 & 9	3	0

Table 2. Fungicide programs with captan for the season. More than 12 applications may be needed. All fungicides with difenoconazole (Quadris Top and Aprovia Top) max 4 apps per year, Switch max of 3 apps per year, Cabrio max 6 apps per year and Captan max 3 apps per year.

Week	With captan
1 (first flowering)	Quadris Top
2	Switch
3	Captan + Cabrio
4	Aprovia Top
5	Switch
6	Captan  + Cabrio
7	Aprovia Top
8	Switch
9	Quadris Top
10	Captan + Cabrio

Other management strategies could include host resistance. Based on a report from South Carolina, Table 3 outlines some cultivars that showed reduced disease development. None of these cultivars are suitable to Ontario production, however it does demonstrate that there may be some genetic resistance in commercial cultivars that could be incorporated into northern cultivars.

Table 3. Cultivars tested in South Carolina against Colletotrichum scovillei

Resistant (0% incidence)	Tolerant (2-5% incidence)	Susceptible (>10% incidence)
Roulette	Mexican Sunset	Cornito Giallo
Red Ember	Mexican Sunrise	Escamillo
Aiji Rico	Chili Pie
	Just Sweet

Pepper growers should keep anthracnose at the top of their mind as planning continues for the 2022 field season. Reach out to myself (katie.goldenhar@ontario.ca) or Amanda Tracey (amanda.tracey@ontario.ca) for any questions or concerns regarding this disease.

References

A.P. Keinath, S.H. Zardus, and V.B. Dubose, and G. Rennberger. (2021) Evaluation of All-America Selections peppers, 2020. Plant Disease Management Reports 15: V040.

Farr, D.F., & Rossman, A.Y. Fungal Databases, U.S. National Fungus Collections, ARS, USDA. Retrieved March 2, 2022, from https://nt.ars-grin.gov/fungaldatabases/

Toporek, S. M., & Keinath, A. P. (2021). First Report of Colletotrichum scovillei Causing Anthracnose Fruit Rot on Pepper in South Carolina, United States. Plant Disease, 105(4), 1222-1222. https://apsjournals.apsnet.org/doi/full/10.1094/PDIS-08-20-1656-PDN