Pioneering Hydroponics

Since 1976

5 Most Common Plant Diseases in Hydroponics - Part 2

In part 1, we looked at powdery mildew, grey mould, and root rot. In this second part, we’ll give an overview of iron deficiency and downy mildew, two other common plant diseases every grower needs to keep an eye out for.


Iron Deficiency

Plants need iron to function properly and for nitrogen fixing, chlorophyll and enzyme production, metabolism, and development. A deficiency of this nutrient starts with yellow leaves and ends in plants dying off if not treated accordingly.

An iron deficiency can present a symptom commonly called leaf chlorosis, which translates into the plants’ leaves turning yellow while the veins stay green. You’ll usually notice leaf chlorosis starting at the ends of new growth before it works itself to older leaves.

Iron deficiencies in plants can be related to issues such as:

  • Too much clay in the soil. Clay doesn’t have a lot of organic material, which plants need to be able to take iron in to their roots.

  • pH level of the soil is too high. Should the soil pH level be higher than 7, or alkaline, it will restrict plants’ ability to get iron.

  • There is too much phosphorus in the soil. High levels of phosphorus can block iron uptake and lead to leaf chlorosis. 

  • The soil is compacted or overly wet. This leads to the roots not having enough oxygen, which complicates iron being taken to the roots.

We recommend a pH meter to ensure you always know the pH level of the medium.


Downy Mildew

Downy mildew occurs in moist environments; this infection can typically be recognised due to faded or yellow spotting that appears on plant leaves. Although downy mildew spreads similarly to a fungal infection and has similar traits to fungal development, it’s an oomycete microbe that lives off plants’ water supply.

Spreading through spores that latch onto leaves’ underside, downy mildew penetrates the surface of leaves with its mycelia before it starts to grow. The upper side of the leaves start to show spots while the underside sees a mat of sporangia form. This can range from white and grey to purple-ish, releasing more spores into the grow room.

As plant matter rots away, more spores are dispersed, destroying stems, leaves, and flowers of plants. The spores can overwinter and remain in the soil for up to 5 years.  

Some symptoms of downy mildew can be:

  • Stems developing reddened areas.

  • Extreme cases leading to defoliation.

  • A grey-coloured, downy coating on the undersides of leaves.

  • Angular blotches from purple to brown to yellow, or even similar to a scorch-like burn.

The disease cycle of downy mildew

  • Spores are produced only on living plant matter.

  • The fungus survives as resting spores in plant debris or infected plants over unfavourable periods.

  • Any cuttings taken from infected plants will carry over the disease to other plants.

  • 85% relative humidity levels help downy mildew thrive.

  • Downy mildew’s optimum temperature is 18℃.

  • Spores germinate in water in just four hours.

Splashing water spreads the spores, unlike powdery mildew that spreads through wind. Temperatures below 11℃ prevent spores from germinating and temperatures above 28℃ kill the spores, if exposed for 24 hours.

Keeping relative humidity levels below 85% is vital to stop germination on healthy plants and decrease sporulation on infected plants. To help control downy mildew, there are a few steps you can take:

  • Apply preventive disinfectants.

  • Follow stringent hygiene and sanitation procedures.

  • Only take cuttings from plants that have never suffered a downy mildew infection.

  • Discard of infected plants immediately, without composting it.

We recommend Silver Bullet for preventative disinfection measures.

If you have any questions about hydroponic nutrients, make sure to get in touch with us on 01695 554 080 or 01226 320 850. You can also purchase some of the UK’s leading brands in hydroponics by finding a shop near you.