Pea plants turning yellow? Season's end, wet roots, mildew or virus

Peas that yellow late in the crop, in warm weather, are usually finishing; yellow lower leaves with a soft stem base mean wet roots, a white coating means powdery mildew, and mottled leaves point to a virus. Where the yellow starts and what the stem looks like sort the cases in a minute.

For sowing dates, pot size and support, see growing peas in containers. For yellowing across other plants, the yellow leaves cause finder is the wider guide.

Start with the calendar and the pod count

Penn State Extension is blunt about the end of a pea plant: when it turns yellow, it is time for it to go. A plant that has cropped for several weeks and fades evenly is finishing, not sick.

Heat speeds the finish. UConn Extension says peas do not do well in higher temperatures, and gives 55 to 70 degrees F as the growing period in which most varieties reach maturity in about 60 days. The University of Maryland Extension puts the favoured range at 65 to 70 degrees F and says plants do not grow well in hot weather. A pot on a sunny balcony runs warmer than a bed, so a late-spring warm spell can end the crop early. Neither source says heat itself turns the leaves yellow, so treat it as the likely backdrop and still check the stem and roots.

If the plant is clean, Penn State says it may be cut at ground level with the roots left in the soil, because peas store nitrogen from the air in their roots. If any of the problems below is present, pull the whole plant instead.

Yellow lower leaves and a soft stem: the roots

UConn Extension says that wilt and root-rot diseases show as yellowing and wilting of the lower leaves, stunted growth, and brown, black or red mushy stems. The University of Minnesota Extension describes one of them, Aphanomyces root rot, as yellow, stunted shoots that may wilt, a brown soft stem at the soil line and soft rotten spots on the roots, most common in heavy wet soils.

In a pot, heavy and wet is a matter of drainage. Lift the pot: a heavy one days after watering has a drainage problem. Check that every hole is open and that the saucer is not holding water. UConn says well-drained soil lessens the possibility of wilts, and that if seedling decay, wilt or root rot has been a problem before, you should change location or improve drainage. For a pot, that means fresh mix, not the old mix again.

Press the stem base: soft and brown means rot, and a firm stem sends you back to your watering routine. The Maryland advice is to keep the root zone moist by watering deeply and regularly in dry periods, not to keep it wet. Overwatered vs underwatered separates the two, and how to save a potted plant with root rot covers what a rotted root system can and cannot recover from. A mushy stem base on a pea plant is a reason to pull it.

White coating: powdery mildew

Penn State Extension names powdery mildew and damping off as the two primary diseases of peas. The University of Minnesota Extension describes powdery white fungal growth that forms spots on or completely coats leaves, stems and pods, and says it is most common on late-planted or late-maturing plants.

Penn State says applying water to the soil rather than from above may reduce the risk of disease. UConn says powdery-mildew-resistant varieties are best for fall planting. A sowing that gets going early is the main defence on offer from these sources, which is one more reason to sow as soon as the mix can be worked. The same fungus family on squash is covered in white powder on zucchini and cucumber leaves; peas have their own species, so follow the pea advice here.

Mottled leaves: virus, and the aphids that carry it

The University of Minnesota Extension lists two viruses of peas, both of which turn leaf veins yellow or white and give the leaves a yellow-to-white mottled or mosaic pattern. Plants may be stunted, pods reduced and malformed, and premature death may occur. UConn says aphids rarely damage pods but may carry one of the viruses that affect peas.

Check the growing tips for small, soft, green insects. Minnesota says large numbers feeding on leaves can cause wilting or death of the plant. For identification and handling, see aphids on indoor herbs. If a plant is mottled and declining, remove it rather than hope.

Yellow with brown spots: a blight

UConn Extension describes Ascochyta blight, a complex of three fungi that survive winter in plant debris or arrive on infected seed: plants show yellow foliage, brown spots on leaves and stems, and bud drop, and the stem blackens from the soil line up. UConn says to remove and dispose of infected plants as soon as the disease appears and to rotate peas with non-susceptible crops yearly. In a pot, the equivalent of rotation is fresh mix and a different crop in that pot next.

Sources

• Penn State Extension, “A Gardener’s Guide to Peas”
• UConn Home Garden Education Center, “Peas”
• University of Maryland Extension, “Growing Green Peas in a Home Garden”
• University of Minnesota Extension, peas: discolored leaves
• University of Minnesota Extension, peas: stunted plant