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Bacterial Leaf Spot

Bacterial Leaf Spot

Xanthomonas species

Bacterialalso: Bacterial spot

A common warm-weather bacterial disease of tomato and pepper that peppers the leaves and fruit with small dark spots. In wet, humid seasons it spreads fast and can defoliate plants and scar fruit, making it one of the harder garden diseases to control because bacterial diseases have no cure once established.

🔎 How to spot it

Look for small, less than one eighth inch, dark brown circular spots on the leaves. On tomato the spots often have a yellow halo and the centers may drop out leaving small holes; on pepper the spots lack a halo. Spots also appear on stems and leaf stalks, and raised scabby spots form on the fruit. Heavily spotted leaves yellow and drop.

🥀 Damage it causes

Leaf spotting leads to yellowing and leaf drop that weakens the plant and exposes fruit to sunscald, while the scabby fruit spots make the fruit unsightly and unmarketable. In a wet season the disease can spread through a planting quickly and sharply cut the harvest.

🔬 What causes it

Bacterial spot is caused by several Xanthomonas species that arrive on infected seed and transplants and survive on plant debris and volunteers. The bacteria spread by splashing rain and overhead irrigation and enter through pores and wounds. Disease develops fast in warm, wet, humid weather at 68 F and above, and slows when nights drop to about 61 F or below.

🛡️ Prevent it

Start with certified disease-free seed and transplants, and use a hot-water seed treatment for saved seed. Rotate away from tomato and pepper for two to three years and clean up debris. Water at the base rather than overhead, space plants for airflow, and never handle or harvest plants while they are wet. Choose resistant varieties where they are offered.

🧯 If it is already here

There is no cure once a plant is infected, so focus on slowing spread: remove the most affected leaves, avoid working among wet plants, and pull severely diseased plants. Preventive copper sprays, sometimes paired with a Bacillus biofungicide, can protect healthy tissue but become less effective where copper resistance has built up; follow the label. Do not compost infected plants.

💡 Good to know

Bacterial spot is easy to confuse with bacterial speck and with early blight, but bacterial spot lesions are small and dark with a shot-hole look on tomato, and the disease thrives in warm wet weather. Because it rides on seed, buying clean seed and treating saved seed are among the most effective steps you can take.

🌱 Plants it affects

357 plants in the library can be affected by this problem

Adirondack Blue PotatoAfrican MarigoldAgapanthusAgeratumAji Amarillo PepperAlice du Pont Mandevilla🥔All Blue PotatoAmethyst Falls WisteriaAmish Paste TomatoAnaheim PepperAnemoneAngelique TulipAngeloniaAnnabelle Smooth HydrangeaAnnual VincaApeldoorn TulipApril Tryst CamelliaArizona Sun Blanket FlowerArugulaAugust Beauty GardeniaAunt Molly's Ground CherryAutumn Joy SedumBachelor's ButtonBanana PepperBarbara Karst BougainvilleaBeach PlumBeauregard Sweet PotatoBecky Shasta DaisyBee Balm🍅Beefmaster TomatoBenarys Giant ZinniaBengal Tiger CannaBetter Boy Tomato🥬Bibb Lettuce🍅Big Beef TomatoBig Boy TomatoBing CherryBlack Beauty EggplantBlack Cherry TomatoBlack Krim Tomato🥬Black Seeded Simpson Lettuce🥕Black Spanish RadishBlack Tartarian CherryBlack-Eyed PeaBlack-eyed Susan VineBlood OrangeBloomsdale SpinachBlue Bird DelphiniumBlue Bird Rose of SharonBlue FescueBok Choy🍅Box Car Willie TomatoBrandywine TomatoBroccoli RabeBrunneraBrussels SproutsBurning BushButtercrunch LettuceButterfly Blue Pincushion FlowerButterfly Marguerite DaisyButterfly WeedCafe au Lait DahliaCalabrese BroccoliCaladiumCalendulaCalibrachoaCalifornia Giant ZinniaCalifornia PoppyCampanulaCardinal FlowerCarolina GeraniumCarolina JessamineCarolina Reaper PepperCascara SagradaCayenne PepperCelebrity Tomato🥬Champion CollardsCheddar CauliflowerCherokee Purple TomatoCherry Belle RadishChicoryChinese BroccoliCleyeraClimbing HydrangeaClimbing Prairie RoseCocktail Vodka BegoniaColeusCollard GreensContender PeachCoral Drift Groundcover RoseCornelian CherryCosmosCreeping PhloxCrimson Cherry RhubarbCubanelle PepperCupani Sweet PeaDaikon RadishDamson PlumDandelionDavid Garden Phlox

For educational and informational purposes only. Disease management advice is general guidance drawn from university cooperative extension sources; always identify a problem positively and read and follow the label on any product before use, especially around food crops, children, and pets.