I cannot determine the cause of just some leaves turning brown and how to treat this issue. Please advise.
Thank you for sending the photo. From what I can see, it appears as though the leaves may have been affected by sunburn. As the plants look reasonably young and will have tender foliage, you will need to protect that tender foliage until the plants are more established. There is an excellent Yates product that we can recommend that will give your plants the protection they need. It is called Yates Waterwise DroughtShield. It will protect plants from heat, water loss, drying winds, sunburn, droughts, frost and transplant shock. It serves as a sunscreen against damaging ultra-violet rays. You will find this product at your local nursery and any of the large hardware stores. I can see you have a mulch around your plants, so watering your plants on regular basis as well as applying the Yates Waterwise DroughtShield will give them a good start and also the protection they need for the hot summer months ahead.
From your friends at Yates Gardening
Answered: 31 Dec, 2011