The technical term for this is ‘Pica’ which is defined as ‘the eating of non-food items’. Causes for pica can be similar to that of coprophagia (eating feces), and can range from normal exploration to actual medical condition (luckily, less likely).
Young dogs often go through a stage of exploration and as part of this put lots of different things in their mouths to chew. Puppies simply love to chew everything! And sometimes this can include things that are even less desirable than your shoes!
The most important tip for puppies exhibiting this behavior, is not to punish the act, but rather offer alternative things to chew and play with. Positive reinforcement of good behaviours always sticks with your dog better than punishment of the bad. This has been proven in many dog behavioural studies.
There can be a few other causes of pica, such as simple boredom or the fact your dog likes the taste. Addressing the boredom with regular exercise, toys, digging pits and lots of affection can sometimes solve the problem. It can also be due to behavioral problems such as attention seeking behavior, a rare compulsive disorder condition or generalised anxiety.
Medical problems such as anemia, malnutrition or malabsorption, endocrine disease and bowel conditions are rare causes of pica. Dietary deficiency is another rare cause and most commercial pet foods are balanced for the needs of your pet.
Dogs that are on medications that increase appetitie can also have this problem.
Always ensure your dog is wormed regularly, both to avoid the problem starting and to treat GI parasitism that can result from regular coprophagia.
It is best to discourage dogs from eating dirt, as although it is unlikely to cause a serious issue, there can be chemicals within dirt that can be potentially harmful. Slug bait is one of the more common ones.