Pests & Diseases

by Sally Arant

Primula in Alaska are not as badly affected by pests and diseases as those in warmer locales. Many problems can be avoided simply by proper cultivation and maintenance. A healthy plant will always be better able to ward of pests and resist disease than an unhealthy one. A young plant is also often better able to survive adverse conditions than an old one, so it is wise to keep stocks rejuvenated through seeding and division.

The vine weevil is the worst pest known to attack primula, but it is less common here than in warmer environments. They prefer soils that are peat based, rather than leaf or animal manure compost based. Larvae will eat the roots of primula right below the crown until there are no roots left to sustain the plant. Check all potted primula brought in from out of state for signs of larvae in the soil and, if found, hand pick them out and isolate this plant from others for observation. Nematodes applied in summer will eradicate vine weevil. It is best to take preventative measures to avoid infestations.

Aphids can be a problem, but they are usually worse on water-stressed plants. Keep plants healthy to begin with, wash any aphids off, and use insecticidal soaps if necessary. Check for root aphids on any plants brought in from out of state nurseries.

Cutworms are often a menace, especially for primula with resting buds above the soil and with very early spring bloom times. Cutworms hide in the leaves and debris around the plants in the fall and winter, stealthily eating away at flower buds. The result may be fewer blooms in the spring, no blooms at all or even death to the plant by the cutworm’s eating of the entire crown. In the late summer and fall, “groom” each susceptible plant by carefully inspecting the plant for cutworms. Simply slice them with a sharp stone or stick. It is a disgusting but very worthwhile fall activity.

Slugs are not usually a big problem for primula but they will often eat only the flowers. Keep slug populations down for the sake of primula and all their companions in the garden.

Primula plants may suffer from viral disease. Symptoms of virus include: distorted, stunted leaves, yellow margins and between the veins, distorted and streaked flowers, stubby roots and general lack of vigor. There is no cure, and plants will only get worse and pass the virus on to others. Remove all virus infected plants. Fortunately, the virus is not passed along to the seed, so it is best to keep stocks renewed by seeding.

Botrytis, associated with hot weather and stagnant air, can also affect primula. Improve the conditions which precipitated the problem (perhaps give the plant a little “elbow room”), remove all rotten parts and apply a fungicide to the affected parts.

Remove all old rotten foliage and debris from around P. auricula and P. x pubescens in the spring to avoid rot.