Corticium blight is an older name still used for two related fungal problems, pink disease and thread blight, that wrap twigs and leaves in fine fungal threads and slowly girdle branches on trees like fig, citrus, coffee, and pepper. If…
Coniothyrium canker and dieback is one of the most common reasons a healthy-looking rose cane turns brown and dies from the tip down, often within a single growing season. If you already spend time pruning your roses each spring, this…
Coniothyrium leaf spot is a fungal disease best known for scarring yucca leaves with sunken brown lesions, though the same genus of fungi causes similar leaf spots on agave, dracaena, and a range of other landscape and houseplants. If you…
Constriction canker is a fungal disease of peach twigs and buds caused by Phomopsis amygdali (synonym Fusicoccum amygdali), named for the way small cankers form around leaf scars and slowly constrict, or girdle, the twig until it dies. It is…
Copper spot is a summer turfgrass disease that covers susceptible grass with small, circular, copper-colored patches, most noticeable right after a fresh cut. If copper spot shows up on your lawn, understanding what makes it worse will help more than…
Corm rot is a general term for several fungal diseases that turn the underground storage structure of plants like gladiolus, crocus, saffron, and taro soft, discolored, and unable to sprout. If a corm rot problem is destroying your bulb-like plantings,…
Common smut is one of the most recognizable diseases a home gardener or field grower will ever see on corn, because there is no mistaking a swollen, silvery gall bursting open into a cloud of black powder. If you are…
Columbia lance nematode, Hoplolaimus columbus, is a microscopic root-feeding worm that lives in the soil and damages plant roots from the outside and from within. It is best known as a problem in cotton, soybean, and corn fields across the…
Colletotrichum is best known for the leaf spot form of anthracnose, but the same fungal genus can also attack stems, shoots, and crowns directly. This form shows up as sunken cankers, dieback of shoot tips, and internal browning at the…
Colletotrichum leaf spot is a fungal disease caused by species in the genus Colletotrichum, the same group of fungi responsible for anthracnose on trees, shrubs, vegetables, and turf. It shows up as small, sunken spots with distinct borders, and on…
A plant that suddenly wilts and dies even though the soil looks fine and the roots seem intact often has a problem hiding right at the surface, where the stem meets the soil. That narrow band is called the collar,…
A tree or shrub that suddenly declines, loses limbs, or fails to leaf out in spring often gets blamed on drought, winter injury, or old age. Sometimes the real cause is underground and has been there for years: Clitocybe root…
A clematis that goes from lush and flowering to black and collapsed within a few days is alarming enough that most gardeners assume the worst. The good news is that clematis wilt, despite the dramatic collapse, is rarely fatal to…
Cladosporium leaf spot is one of those diagnosis names that covers more ground than most gardeners expect. It is not a single disease of one plant, it is a description of what happens whenever a fungus in the genus Cladosporium…
Citrus scab looks worse than it usually is. The first time I found wart-like bumps crawling across a young grapefruit leaf I assumed the tree was in real trouble. It was not. Scab is almost entirely cosmetic, it only ever…
Citrus greening is the one citrus problem where I do not tell people to try a few things and see how the tree responds. It is a bacterial disease, it has no cure, and a tree that has it will…
The first sign of citrus greasy spot is a tree that looks tired for no obvious reason. Nothing dramatic happens to the fruit. Nothing dies back. The older leaves just go blotchy, then yellow, then they are on the ground,…
A papaya is not a tree. It is a giant soft stemmed herb that happens to grow taller than you do, and once you accept that, almost everything about how to grow papaya fruit starts to make sense. It sprints…
I planted my first tangerine because I wanted fruit I could peel with one hand. Two winters later I understood that the tree is the easy part and the calendar is the hard part. Getting sweet fruit off a tangerine…
The first mandarin I ever planted came from a supermarket seed I sprouted in a yoghurt pot. I looked after that tree for six years before I understood it was never going to fruit in my lifetime. The second was…
