Plant Pathogens and Disease

Pathogens are microorganisms that cause disease in living things, including plants. There are four main types you need to know: viruses, bacteria, fungi, and protists.

Let's look at some real examples. Rose black spot is caused by a fungus that specifically targets roses, creating those dark spots you might've seen on rose bushes. The tobacco mosaic virus doesn't just infect tobacco - it also attacks tomatoes and peppers, showing how some pathogens can jump between related plant species.

It's worth noting that not all plant problems come from pathogens. Aphids are tiny insects that damage plants by sucking sap from their stems, but they're pests rather than pathogens.

Quick Tip: Remember that pathogens are microscopic disease-causers, whilst pests like aphids are larger organisms that physically damage plants.

Nutrient Deficiencies in Plants

Plants need specific nutrients to stay healthy, and when they don't get enough, they show clear warning signs. Magnesium is essential for making chlorophyll - without it, leaves turn pale green because they can't produce enough of that vital green pigment.

Nitrogen (found in nitrates) is equally important as plants use it to make proteins for healthy growth. A nitrogen shortage also causes leaves to go pale green, making it tricky to tell magnesium and nitrogen deficiencies apart just by looking.

Both deficiencies seriously mess with photosynthesis, reducing the plant's ability to make food and grow properly. This explains why pale, sickly-looking plants struggle to thrive.

Spotting Plant Disease Symptoms

Plant diseases create a whole range of symptoms that are fairly easy to spot once you know what to look for. You might notice stunted growth where plants stay smaller than they should, or spots on leaves like those caused by rose black spot.

Other telltale signs include decay of plant parts, malformed stems or leaves, and general discolouration. The presence of pests like aphids can also indicate that a plant is under stress.

Learning to recognise these symptoms helps you identify problems early and take action before diseases spread to other plants.