I have several colors of lantana bushes, now three years old , growing well and up to 5 ft tall They get nearly full sun and generally good water ( an edge with shade has azaleas that have a high water demand and are doing well). About 90+% of the flowers never bloom. The flower buds form and then turn black while small . It is black, not grey , no fuzz , just small black "would have been flowers" buds. A low yellow variety only loses about 70% of the blooms. Last year and earlier this year , I assumed the deer were eating the buds : About 2 months ago I put up a temporary 42 " fence ( the deer don't jump it because they have no clear areas to land). Since then I looked more closely and see the flower buds are black and shriveling. Nothing else shows a problem; there is Rosemary, Pride of Barbados, Oleander, Gardenia, Camellia , Aloe , trumpet vine (invasive) small peach tree , grassy weeds, and a couple that I forgot.
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Anecdotally, from other gardeners (I can't find anything that mentions this on line) I have heard that Lantana buds do this when they're getting too much water (rain or sprinkler especially) - could that be an issue? Other times, its the seedpods turning black once mature,but that only happens later, if the flowers actually open – Bamboo Sep 11 '19 at 20:38
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We have had a relatively hot dry summer. I have watered occasionally , often when the shade azaleas look like they need water. You made me realize there have been essentially no seed pods in 2 years. – blacksmith37 Sep 12 '19 at 00:54
2 Answers
You could have a very common disease of Lantana: Yellow Aster Disease
Not great news for your shrubs however. I guess Western Australia has classed Lantana as a very bad WEED. Let me know if this article speaks to you. Do the flowers kinda look like broccoli before they go black?
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The link you posted is a 451 - inaccessible by people outside of America, or certainly not by people in Europe.. However, I thought Aster Yellows made flowerbuds look vaguely similar to cauliflowers rather than making them go black, as well as making the foliage look yellow in parts? I checked it out on another site that is accessible – Bamboo Sep 11 '19 at 23:17
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Yes and no. I have no broccoli- like heads but mine look very much like the two flower buds at the right side ; one has a flower and the second looks dead . – blacksmith37 Sep 12 '19 at 00:54
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@blacksmith37 I can't comment because I can't access the link provided... – Bamboo Sep 12 '19 at 10:47
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Removed the unnecessary deer fence and examined the lantana . Definitely no cauliflower , broccoli, or brussel sprouts but I suspect the problem is some variation of Yellow Astor disease.Very little insect activity , although several spiders with webs about 4 ft above the ground. Because the folieage looks so good , I will cut and remove all branches this fall and hope for the best in the spring . – blacksmith37 Sep 12 '19 at 18:23
Looking on the web for @stormys' answer : I find "yellow aster " affects many plants in many ways. The common thread is that it attacks the reproductive systems, and as answered there is no reasonable cure. So I will cut all the lantana and burn ( as weather permits) the wood. Keep an eye out for strange growths at any flowers. There is a chance the disease came in with a package dahlia bulbs I got from a discount store ; the flowers were small and the plants died out in early summer.
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I have seen a "wild" lantana about a block away in an unused lot , so no care . It is blooming and seeding very well ; apparently no Aster disease. – blacksmith37 Feb 12 '20 at 17:03