Problems with Peonies
As plants and as a crop, it’s not surprising to hear peonies have various pests and diseases that need combatting. Fungal, insect, and bacterial infections are not unheard of, nor are a variety of conditions peonies can get simply from mistreatments in the spring. Fortunately, our farm is here in Alaska; there are few pest, fungal, or bacterial infections we need to sweat over. However, that’s not to say there are NO problems here under the midnight sun. So, let’s look at the top 3 issues Alaska peony farms face.
Cabbage heads.
So this is actually the most significant problem here in Alaska — and it’s not even a disease. Cabbage heads are malformed peony florescence that disfigure the flowers. Also called “bull-nose,” “cigar,” and “flat-top” buds, this is usually the result of damage during the early stages of bud development. Severe weather, crushing, or insect damage will cause a cabbage head. There is no cure for this. To prevent cabbage heads, guard and protect your buds until they are mature enough to stand independently.
Usually, this is not endemic in our fields; we get relatively mild weather with little to no hail, heavy rains, or sudden, late frosts — insect damage is rare, also. However, finding at least one cabbage head in each variety we grow is not unusual.
Botrytis
This is a severe problem in much of Alaska — particularly along the wetter, cooler coasts. Also known as grey mold, botrytis is a genus of fungi in the family Sclerothiniaceae, a hyphomycetes that includes over 30 varieties. This particular monster is a crop killer over a vast array of different cultivars (fruit, greens, etc.) and is a severe problem for peonies in Alaska as Alaska is, low and behold, a humid, cool, wet climate where foliage is almost always wet through the growing season. In severe infections, entire plant matter can be lost to the fungus — in more common situations, the bud will usually rot (but rot/wilt) before it can fully develop. Browning on the leaves and stems is also typical; the leaf usually looks dried up or burned.
Botrytis has no cure; you can only act to prevent it. Usually, the fungi can’t establish itself in a given area here in Alaska UNLESS given the opportunity — which we never do. The best advice is, in the autumn, when peony stems are beginning to die back after the frost, cut them out and burn them, process them, or toss them far away from your peony beds. You see, botrytis lives in the plant matter; it will winter over in the stems and leaves and reinfect the plant next year. It’s not fatal, but it will destroy your flowers if it is not dealt with.
Some growers are inclined to spray; I try to avoid this, but I will if necessary. Organic sprays include copper fungicides and sustainable blends of active Bacillus subtilis, which infects and kills the fungus. Harsher chemicals can be used, though I rarely recommend them; you should act to prevent infections rather than stop them.
Thrips
There is only one major pest in Alaska that will actually do damage to peonies — and that’s thrips. Order Thysanoptera, thrips are tiny sucking insects that feed on plant matter via punching the flesh and sucking out the sap. We have green thrips, and though, under normal conditions, they are not a problem, exceptionally high population years that are a NIGHTMARE. They have serious sweet tooths, and seeing peonies drip sweet sap from their buds pre-bloom, they flock to the fields. Their means of feeding can cause severe damage to the peony bud, resulting in malformed fluorescence and, potentially, cabbage heads.
Some pesticides will do away with thrips —- I’ve never used them, but a regular, organic aphid spray will put them out during their reign of terror (for us, May - July). They have never been such a problem that I needed to spray — but I keep it in mind if we have a population boom. Usually, I encourage predation insects in the fields that will feed on the thrips and keep their numbers down — let nature take care of it and all that.