Gadenin日本語Get the appAphids in the growing tips
Aphids are the most consistent chrysanthemum pest and they colonise the softest tissue, which means the growing tips and the flower buds. On a fed, well watered plant in spring there is a great deal of soft tissue, and a colony that starts as a dozen insects on one tip can cover every shoot in three weeks. The damage is distorted, puckered new leaves, buds that open lopsided or fail to open, and sticky honeydew that black sooty mold then grows on.
Aphids also carry virus between plants, which is the more serious problem in the long run. A plant with virus shows stunted growth, mottled or streaked leaves and flowers that come small and distorted year after year, and there is no cure. That plant should be dug up and destroyed, not divided, or the divisions carry the problem into the rest of the bed.
Check the tips weekly from spring onwards, turning a couple over to look underneath. Early on, squashing them between finger and thumb genuinely works. For a heavier infestation, a firm jet of water knocks them off, repeated every few days, and an insecticidal soap deals with the rest. Overfeeding with nitrogen makes the plant far more attractive to them, which is one more reason to stop the nitrogen by late summer.
Leaf miner: pale winding tunnels inside the leaf
Chrysanthemums have their own leaf mining flies, and the symptom is unmistakable: pale, meandering tunnels running through the thickness of the leaf, widening as they go, with a small dark larva at the leading end. The tunnels are inside the leaf, so nothing sprayed on the surface reaches the insect.
The damage is cosmetic on a healthy plant carrying plenty of leaves, and a badly mined plant loses enough leaf area to flower poorly. The effective control is simply to pick off mined leaves as soon as you see them and put them in the bin rather than the compost pile. Doing that consistently through early summer keeps the population from building through successive generations.
Adults are tiny dark flies that lay eggs in rows of small pale punctures along the upper leaf surface. Those punctures are visible a week or so before any tunnel appears, and removing the leaves at that stage is the cheapest control there is.
| What you see | Likely cause | What to do |
|---|---|---|
| Puckered, distorted new leaves at the tips | Aphids on the growing points | Check under the tips, wash off or use insecticidal soap |
| Pale winding tunnels inside the leaves | Leaf miner larvae | Pick off and bin affected leaves, keep checking weekly |
| Lowest leaves with dark brown blotches, spreading up | Chrysanthemum leaf spot | Strip affected leaves, water at the base only, open up the plant |
| Fine pale stippling and webbing under leaves | Spider mites in hot dry conditions | Raise humidity, water properly, wash the undersides down |
| Ragged holes chewed in petals overnight | Earwigs feeding after dark | Trap in a straw filled pot on a cane, empty each morning |
| White powdery coating on upper leaf surfaces | Powdery mildew from dry roots and still air | Water deeply, thin crowded stems, avoid wetting the leaves |
| Stunted plant, mottled leaves, distorted flowers each year | Virus, spread by aphids | Dig up and destroy. Do not divide or take cuttings from it |
Brown lower leaves: leaf spot, drought, or just age
By late summer almost every chrysanthemum has some brown at the bottom, and the three causes need three different responses. Chrysanthemum leaf spot appears as dark brown or black blotches with a yellow halo, starting on the lowest leaves and climbing the plant leaf by leaf after wet weather. Drought damage is a dry, papery browning from the leaf edges inwards, affecting the lower leaves first because they are oldest. Simple age is a clean yellowing of the very lowest leaves only, which then drop, with nothing spreading upwards.
Leaf spot is splashed up from the soil by rain and by watering, so the whole of its control is about keeping water off the foliage and keeping air moving. Strip the affected leaves and bin them, mulch the soil surface to stop splash, water at the base, and do not let plants stand shoulder to shoulder. Clearing away all the old top growth in late autumn removes the spores that would otherwise overwinter on it and start next year's cycle.
Spider mites are the other late season problem, and they are a symptom of the plant being hot and dry rather than a random arrival. Fine pale stippling on the upper surface with faint webbing underneath is the sign. Watering properly and hosing the undersides down every few days breaks them, and a plant kept adequately watered rarely gets them at all.
Bin diseased chrysanthemum foliage rather than composting it. Leaf spot and mildew both survive perfectly well in a domestic heap that never gets hot enough, and come straight back on next year's mulch.
What to record, and when to give up on a plant
Write down the date you first saw each problem and on which plant. Most chrysanthemum trouble arrives at roughly the same point in the season every year in a given garden, so a two year record turns the whole thing from reaction into prevention: you know to start checking the tips a fortnight before the aphids usually appear, and to strip the lowest leaves before leaf spot normally starts climbing.
Note which plants recur as problems, too. A clump that gets leaf spot badly every single year while its neighbors stay clean is usually sitting in a spot that stays damp and still, and moving it at the next division solves what no spray will. A plant showing the stunted, mottled, distorted pattern of virus is the one case where the answer is to remove it entirely, and the earlier that decision is made, the less chance it has to be spread around the bed by aphids.