One observation about your watering schedule that could be responsible for a number of problems that include insect attack & disease issues: if your soil remains moist for a week, it is inappropriate for container culture. Soils should drain quickly & require watering at least every other day in the warm months - every day is better.

Fine roots that primarily absorb water & nutrients, begin to die quickly, within hours when deprived of O2. When enough water is used from the soil and adequate air returns, roots begin to regenerate. This seesaw death/regeneration of roots is taxing from an energy use perspective & causes the tree to use energy that could be directed toward keeping the tree's systems orderly, fighting off insects and pathogens, or being allocated toward production of biomass.

The leaf yellowing is likely an issue created by soggy soil. Saturated soils that drain poorly also bring other issues aside from nearly inevitable root rot. The low oxygen levels associated with these soils cause iron and manganese to become electron acceptors. This leads to their precipitation (iron and manganese) and, even though these elements might be present in soils, the plantÂs inability to assimilate them.

Soils are the foundation of any planting and it is imperative that it be a firm one (foundation) if you wish the planting to grow with anywhere near its potential genetic vigor.

Al

Also, I think you're feeding your lemon tree too much. Excess fertilizer can burn roots. I'd cut back and feed once a month. What type of food are you using? When you fertiize, do you follow container directions? If the bottle suggests feeding once a month, do you divide in half when using every other wk?

Was the fungicide was it a foliar spray or someting in the soil? If foliar, never apply chemicals on sunny days or place somewhere they won't get direct sun after an application.

Make sure your soil contains nutrients, but is well-draining, too. Water soil when it needs it. In other words, don't add water once a wk..Do so when, at least, the top 3" feels dry. Actually more than that..

What size pot is your lemon in? Watering depends on many variables like heat, humidity, room temp, sun, etc. But the best way to check is either stick you finger in the soil..if it comes out moist, wait a few days and recheck. If dry, then give it a good drink..You want to water thoroughly, until water seeps out of draingae holes. But before watering the next time, check the soil. Lifting the pot tells you weather or not soil is wet or dry too. Lift pot when the soil is dry. Feel its weight. If it's light then soil is dry..if heavy then soil is wet. This is a sure way to tell, but not good for your back..LOL. Toni

thanks al and toni. the information given, i believe will be very helpful to me. al and toni the fungicide (folair spray) was used as a preventive and not in response to a particular problem and was applied at night. other than the yellowing of the leaves and the brown patches the seedling has been relatively problem free. the fertilizer that i am using is miracle grow (recommended feeding 7-14 days. toni, yes i am following the instructions as to the feeding of the tree no deviations. not sure of the size of pot but it's a very big pot 22 inches across the top

well Gia from what you say about using miracle grow i would say it wouldnt hurt if you flushed your soil...like hopeful said the excess fertilizer may be burning your roots...also chemical fertilizers are notorious for causing salt buildups...

Sorry to be redundant, but you rarely get fertilizer salt build-up in appropriate container soils. You cannot fertilize on a schedule. Dose intervals depend on how fast soil drains, time of year, light conditions, temperature, plant size relative to soil volume, watering habits ... . In summer when the plant is growing well & you're watering daily, a weekly feeding might be appropriate. In winter, with a resting tree, you might not need any fertilizer from Oct to Apr, all depending on where you live & the cultural conditions outlined above.

If your soil drains well enough so you can saturate the soil at each watering, and that 10-15% of the total water applied escapes through the drain hole - salt build-up and over-fertilizing is rendered a non-issue. Gia may actually not be able to flush her soil without risking rotted roots if she is able to go a week between waterings.

Al