Butterfly Bush Dying?
To whom it may concern, last year I planted a dwarf Butterfly Bush called Miss Violet. I have clay soil and don’t apply any mulch or compost to the top soil. This spring I had some leaves yellow that were mostly at the bottom of the bush, so I watered it and fertilized it with miracle grow (non liquid). I did this twice this spring. Then, there was holes in the leaves that appeared to be spider mites, so I sprayed it once with Bayer Disease Control. After a week, the problem got worse so I took the leaves to the nursery and they confirmed it was spider mites. Then, two days ago I sprayed the bush with All Seasons Horticultural Spray Oil. Now, it looks like the bush is dying. I had to cut an entire branch this am because it died. I just gave the bush miracle grow again with one watering can of water. It rained last Thursday in MD. Please help me as I don’t want this beautiful bush to die!!! On a side note, I had a Bee Balm Plant next to it and it recently died of a disease. I’m feeling very discouraged. Thank you! Lisa L.
Howard County Maryland
Butterfly Bushes are rapid growers (though semi-dwarf varieties such as this are a bit slower) and, in general, it is not uncommon for them to shed older, lower leaves that are now being shaded by the lush upper growth. While nutrient deficiencies can also cause lower leaf yellowing in plants, Butterfly Bush are very tolerant of nutrient-poor soils and should not need supplemental fertilization (at least not regularly). Their tolerance for such soils and relative pest-free nature are one reason why some varieties (not this one) can successfully become weeds of disturbed wild areas.
We do not see signs of leaf yellowing in the first photo, if that is a recent picture. In fact, the plant looks quite good overall and healthy.
Spider mites can afflict Butterfly Bush, but tend not to pose a serious problem. Their feeding style does not cause holes in foliage. The mites would primarily create fine webbing around the joint of the leaf and the stem and a fine stippling of the leaves - like a misted look, but missing some green color.
The browning, burning, and tearing visible in the other photos is not caused by mites. This spring's weather was very conducive to a range of fungal leaf diseases and even outright cold damage to young, vulnerable leaves during overnight cold snaps. Neither is serious to the plant's health and damaged leaves can be clipped off.
Disease-controlling treatments do not affect insects and are not intended to be used as insecticides; this is why your first spray had no effect. (Damaged leaves will also not heal, even if the problem is corrected. Instead, new growth is what is being protected and should stay "clean" and healthy if the spray is working.) Your second treatment with oil should have helped with any mite problems, but only if it was used to thoroughly coat all leaf surfaces - upper and lower, which is tricky to do. Re-treatment will be needed if mites are present in high numbers, as spider mites thrive in hot, dry summer weather. That said, as a pollinator plant, it would be best to not spray this bush at all, if possible. At the very least, do not spray the flowers, and no sprays should be used during temperatures above 85 degrees F.
Phytotoxicity is a condition of tissue damage from chemical sprays on plants. It can happen even with plant-safe sprays when they are applied in inappropriate weather (such as the heat mentioned above). They can also cause damage when combined inappropriately; package labels will give caution about this if it applies. More information about this phenomenon can be found here: https://extension.umd.edu/hgic/topics/phytotoxicity. Plants outgrow this damage if exposure is not repeated. The leaf burn in the second photo does look suspiciously like it might have been caused by this, although drought stress is another possibility.
If an entire branch died, that could be simply broken stem tissue from weather or wildlife, or something else. Without a sample to look over, we cannot tell what the cause was, but given the overall appearance of the plant in the first photo, it is probably nothing serious.
Discontinue fertilizing, as this can help spider mites to breed and prosper. Plus, the plant doesn't need it and is not showing signs of nutrient deficiency. Soak the root zone well when it needs water, but otherwise let it dry out some between waterings. The best way to monitor for this is to feel the soil near the roots a finger's depth (or trowel depth) down and see how moist it is. Soil that is sufficiently damp will feel cooler and easily stick to your finger; it will also usually look darker. Drier soil will feel warm, be easily dusted off, and be a similar color to the surface soil. Butterfly Bush has good drought tolerance and should not be kept constantly damp. Over-watered plants start to suffer root death from lack of sufficient oxygen in the soil. When roots cannot supply all of the foliage with moisture, some of it is shed or suffers "burns" from dehydration and overheating.
Mulch covering the soil over the roots would help minimize the heating of the surface soil during the day, protecting it from evaporation as well as weeds that would compete with the plant.
The loss of the Beebalm was probably unrelated to any stress factors affecting the Butterfly Bush. Beebalm often contracts powdery mildew, an unsightly leaf disease but not often a fatal one unless extensive and untreated for a prolonged time. It may have contracted a root disease if over-watered, but Beebalm have better tolerance for moist soil than many other garden plants.