Black spot on peas

I have used bales of pea straw to mulch my garden regularly. From time to time tendrils of self-sown peas emerge, grow a little and then, without my providing any sort of vertical supports for climbing they languish across the mulch. Eventually, slowly, they wither then die. I figure their death is good for the soil and care not.

Some of the mulch has topped earth in a bin in which I hoped robust layers of potatoes would grow. Certainly potato leaves are flourishing through the mulch and therefore I assume that, deep below, potato tubers are growing. Recently my garden was flushed with excessively torrential rain accompanied by an icy couple of days. I think that weather combination is what caused the lone pea tendril in that bin to accumulate black spots.

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In the expectation this was a fungal blight, I pulled the fragile plant out and it has now been thrown into my rubbish bin for destruction. A little googling gave me information which supported my action.  Gardeningknowhow explained that ‘Asocochyta blight, bacterial blight, root rot, damping off, downy and powdery mildew, fusarium wilt, and various viruses are some of the pea plant diseases that may afflict pea plants.’ It was clear that ‘Blackspot is seed-borne or soil-borne and can survive on infected stubbles. Removal of infected field pea trash and volunteers is vital.

Agriculture WA covered the topic in depth for pea farmers and urged them to be vigilant for a disease which ‘initially appears as small, dark, irregular flecks on leaves, stems and pods. Lesions enlarge in rainy and or humid weather’ Stem lesions enlarge to become long, wide streaks that are blue-black or purplish. These often join together too completely girdle stems, leaf stalks or tendrils and kill the plant. The disease damages the base of the stem and blights leaves, stems, pods and flowers’.

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Fundamentally the disease comes from contaminated stubble and wet conditions.

Any one or combinations of three fungi may cause blackspot in field peas. All three can occur together and symptoms caused by each may not be easily distinguished from the other. The organisms involved are: Mycosphaerella pinodes – leaf spot, blight; Phoma medicaginis var. pinodella – foot rot; Ascochyta pisi – leaf and pod spot. Mycosphaerella pinodes causes the most damage to field pea crops in Western Australia, and is the principal pathogen involved in nearly all occurrences of blackspot. Phoma medicaginis is occasionally found on infected stems of field pea. Ascochyta pisi is not common in Western Australia. The fungi can either be seed-borne, soil-borne, or survive in pea trash. Infection may occur at any stage of plant growth. During wet weather the disease may spread rapidly. Spores produced on infected plants are transferred onto adjacent healthy plants by wind and rain splash.

I remain vigilant for any new diseased tendril.

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