Pea Problems: Powdery Mildew, Pea Moth, Aphids and Root Rot

Work out where the trouble is coming from

Start by deciding whether the problem is on the leaves, inside the pods, or below ground, because the response is completely different in each case. Leaf trouble is usually mildew and is manageable. Pod trouble is usually pea moth and is only preventable, never curable. Below-ground trouble is root rot or wilt, and that decides where you can sow next year.

The second question is how far through the season you are. Peas naturally decline as the weather warms, and a row that is yellowing and mildewed at the end of its cropping period is simply finishing, not diseased. Pulling it and sowing something else is a better use of your time than treating it.

Powdery mildew: airflow first, spray second

Powdery mildew arrives as a white dusty coating on the upper surface of the leaves, usually low in the plant, and spreads upwards until the whole row looks gray. Unlike most fungal problems it thrives in warm dry weather with damp nights, which is exactly the condition of a pea row in late spring. Crowded rows and dry roots make it much worse.

Once a leaf is coated it will not recover, so the job is to slow the spread and get the rest of the crop picked. Remove the worst leaves and take them off the plot, open up the row by tucking stray growth back onto the support, and keep the soil moist, since a drought-stressed plant is far more susceptible. A spray of potassium bicarbonate or an approved fungicide, applied at the first white patch rather than when the row is gray, buys you two or three more weeks of picking.

1. Check the lower leaves weekly From the moment flowering starts, look at the leaves in the bottom foot of the row. The first sign is a small white patch the size of a coin on an upper leaf surface.
2. Remove and remove from the plot Take off the worst affected leaves and bag them. Do not drop them at the base of the row or compost them in an open heap.
3. Water the roots, not the leaves A well-watered plant resists mildew far better. Soak the soil at the base and keep the foliage dry.
4. Consider semi-leafless types next season Types with tendrils instead of most leaves move much more air through the row, and many carry genuine mildew resistance.

Pea moth: the maggots in the pods

You find pea moth when you shell the crop: small pale caterpillars, a few damaged seeds, and grains of frass inside an otherwise normal-looking pod. Nothing shows from the outside, which is why it is always a surprise. The moth flies in warm weather and lays its eggs on plants that are in flower, the larvae bore straight into the developing pod, and by the time you see the damage they have already fed and left.

There is no useful treatment once the eggs are laid, so the whole answer is timing and barriers. Peas that flower outside the main flight period escape almost entirely, which means very early spring sowings and late sowings both dodge it while a mid season sowing takes the worst of it. On a small row, fine insect mesh laid over the crop from the first flower until the pods are picked is completely effective, provided the edges are pinned down.

1. Shift your sowing date The simplest fix. Sow very early so the crop flowers before the moths fly, or late so it flowers after them. Note the dates that worked and repeat them.
2. Mesh the row from first flower Lay fine insect netting over the support as soon as the first flowers open and pin the edges to the soil. Peas are self-pollinating, so covering them costs you nothing.
3. Clear the haulm at the end The larvae drop into the soil to overwinter. Pull the spent plants, and do not put peas back in that bed next year.

Affected pods are still usable. Shell them, pick out the damaged seeds and the caterpillars, and use the rest. The damage is unpleasant to look at rather than harmful.

Aphids: the virus is the real problem

Pea aphids cluster on the growing tips, the flower stalks and the young pods, and they are large enough to spot easily, often pale green and sometimes pinkish. A light infestation costs you very little directly. What matters is that they transmit pea enation mosaic and pea leaf roll viruses, and there is no treatment for a virus once a plant has it.

Deal with them while they are still in clusters on the tips. A firm jet of water knocks most of them off, and a squash between finger and thumb handles the rest. Ladybird and hoverfly larvae clear an infestation quickly if you leave them alone, so avoid broad-spectrum insecticide, which kills them and leaves the aphids to bounce back faster than the predators do.

1. Check the tips twice a week Look at the growing points and the undersides of the top leaves. Aphids start there before spreading to the flower stalks.
2. Wash them off early A jet of water directed at the tips removes most of a young colony. Repeat after two days to catch what survived.
3. Pull plants with distorted, mottled growth Yellow mottling, puckered leaves and stunted tips mean virus, not aphids. Those plants will not recover and they are a reservoir for the rest of the row.

Root rot and wilt: a rotation problem, not a spray problem

A plant that yellows from the bottom, wilts in the day and does not recover, then dies while the rest of the row looks fine, has a root problem. Pull it up and look: brown, soft, or blackened roots and a discolored streak running up inside the stem base confirm root rot or fusarium wilt. Both live in the soil, both build up wherever legumes are grown repeatedly, and neither has a chemical cure available to a home gardener.

Everything about managing them happens before you sow. Leave three to four years between pea or bean crops in the same bed. Improve drainage, because these organisms thrive in wet compacted ground, and raise the bed if water sits after rain. Do not compost affected plants in a heap you will spread on the same garden.

1. Lift a failing plant and inspect the roots Healthy pea roots are pale and fibrous with pinkish nodules. Brown, mushy or blackened roots mean rot, and a bed you should not sow peas in again for years.
2. Fix the drainage If water stands on the bed after heavy rain, raise it or work in compost and grit. Waterlogging is what lets root rot take hold.
3. Record the bed and the year Note the bed, the year, and the fact that root rot appeared there. That single line is what stops you sowing peas into infected ground three seasons from now.