Botrytis neck rot, caused by the fungus Botrytis porri, is an uncommon disease in Ontario, but some areas this year have received the cool and wet conditions required to cause disease in garlic fields. There are several species of Botrytis that infect garlic including B. porri, which has been documented to generally infects plants through wounds.
When B. porri colonizes the bulb and crown, lower leaves show symptoms first. Plants appear stunted and green leaves can develop water-soaked lesions, wilt and eventually turn yellow (Figure 1A). Plants infected with stem and bulb nematode show similar symptoms with yellowing of the leaves from the bottom of the plant moving upward, but the leaves turn yellow before wilting (Figure 1B).
When plants are pulled, greyish-brown mould / mycelium is found on the outside necks of plants above the crown (Figure 2 – 3). As the disease progresses, black fungal bodies known as sclerotia up to 7 mm (~1/4 inch) in size form on the outside of the bulb and neck (Figure 4 – 5). The outer wrappers of the bulb break down and secondary infections from other pathogens, like Fusarium or Penicillium can follow. Harvested bulbs with Botrytis neck rot generally have few to no bulb wrappers remaining at harvest.
If only a few plants are found throughout the season, rogue out these plants to reduce inoculum levels. Avoid excessive irrigation and late applications of nitrogen.
The sclerotia can survive on dead plant material and the soil for several years, depending on soil conditions, residue depth, tillage and soil moisture. Botrytis porri is limited to hosts in the Allium family. Development in the field is greatest when cool, damp and cloudy weather persists. Sclerotia germinate under these conditions and release spores that can be carried by the wind to infect new plants throughout the growing season (Crowe 2002).
In storage, Botrytis grey mould survives on the surface of the bulbs or between leaf/wrapper layers and can move between cloves through the bulb’s basal plate (Jepson 2011). Botrytis porri is a weak pathogen that generally colonizes wounds. Reducing the time between cracking / splitting of the bulbs into cloves in the fall and planting is crucial for reducing the chances that wounds created from the cracking process are colonized by B. porri before they are planted.
Fungicides for both conventional and organic production are registered for Botrytis spp. and can be found in the Ontario Crop Protection Hub. Applications should be aimed earlier in the season in fields where Botrytis neck rot has been a problem in the past and if conditions are favourable for disease development.
In summary:
- Plant as soon as possible after cracking bulbs into cloves
- Avoid planting cloves with any fungal colonization
- Dig up suspect plants in the spring with lower yellow leaves and inspect the crown for grey mould or sclerotia
- Incorporate crop residue after harvest and avoid returning to the field with susceptible crops (Allium spp.) for 3 years or more.
By Katie Goldenhar and Travis Cranmer
Crowe, F. (2002). Towards improving control of botrytis dry rot of garlic (Botrytis porri). Central Oregon Agriculture Research Center 2001 Annual Report. 92-97.
Jepson, S.B. (2011). Botrytis rot of stored garlic. Oregon State University Extension Service.
Misawa, Ueno, R., Kurose, D., & Nakahara, K. S. (2020). First report of Botrytis porri causing Botrytis leaf blight on leek in Japan. New Disease Reports, 41(1), 19–19. https://doi.org/10.5197/j.2044-0588.2020.041.019
du Toit, Derie, M. L., Hsiang, T., & Pelter, G. Q. (2002). Botrytis porri in Onion Seed Crops and Onion Seed. Plant Disease, 86(10), 1178–1178. https://doi.org/10.1094/PDIS.2002.86.10.1178C
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